When to do a water change?

[AquaAggie]

Ok so I think I know the answer to this question, but I’m curious to see others thoughts. I was surprised to not find a similar thread already when searching the forum, but

When/how often should you do a water change?

some say every week
some say every 2 weeks
once a month
when nitrates hit 40
”I never do water changes just top offs”
discus owners seem to do it daily 😂

 

So when or how often do you do a water change and why?

[Keeg]

For me, I do water changes every/ every other week and always top off the water whenever it is low. I have a 40g with a low stock of fish, medium amount of plants, and a sump meant for a larger tank, so the water is really clean and I don't have to stress about it. The amount of water changes really depend on the size of tank and its inhabitants. A good general rule of thumb is to do it every week. Test your water periodically to see if you should go an even shorter amount of time. 

[Fish Folk]

Simple and straightforward as the question is, it is not always easy to answer. Probably the _best_ answer is more indirect: Don’t set up more tanks or tanks in certain locations than you can easily do a 33% water change on weekly. However, that’s more to _avoid_ the problems of infrequent maintenance than to directly answer your question. 
 

We set up a little fish room right next to a small 1/2 bathroom. Perfect placement. Easy to stay on top of! But there are tanks in far reaches of our home... not so easy! And once time needed to maintain adds up, it’s easy to fall behind. Oddly, smaller tanks tend to get less care than larger tanks, even though they’re the tanks most prone to chemistry issues. 
 

We do tanks every week / or every two weeks. Usually a 50% change. Some get gravel vac... some don’t. We run about 20 tanks. 

[MJV Aquatics]

The solution to pollution is dilution and you can rarely have too much fresh water. BUT the minimum requirement for volume/frequency depends on stock level, food types, feeding amounts, if you have plants, etc.

I mostly do 50% weekly on some tanks. On heavily stocked tanks I do 50% twice a week. But fish are living in polluted water and if there's no such thing as too much fresh water...well, then there's your answer. If the hobbyist is lazy, the stock likely suffers.

[Maggie]

I do water changes 10-15% twice a week, and double that if I miss one. If I had a 10 gallon going, which I will soon, I'd do 20-30% twice a week. I don't feel it's necessary to do it so often, just easier for me since I don't have a python.

[Kirsten]

Depends on the fish, too. Some, like discus, can be super sensitive to any imperfections in the water. Some, like bettas, are found living (though not necessarily thriving) in stagnant mud puddles in the wild. The amount of plants you have in your tank affects the equation, too. Plants need those nitrates to thrive. So it's sort of a balancing act between what your fish can handle and what your plants need, and vice versa. So I'll tell you what I'm doing right now:

10g betta tank w/ pygmy cories and snails: was hooked up to a bed of hydroponic basil, but it was making everyone miserable, including me. Nitrates were always low, unsurprisingly, considering the number of plants I was trying to keep alive with that water, but my poor betta still got a bad case of fin rot, probably from the stress of having gallons of water dumped on his head for 15 minutes of every hour. So after my basil got mites and taking them out and cleaning them off caused tons of muck to be released into the tank, I'd had enough and tore it down and now it's just a normal 10g. Betta Don Carlo is still on the mend and I've been doing weekly 2-gallon water changes and got him a new piece of spider wood to increase the tannins and apologize to him.

5g with a pea puffer and a live larder of snails: I've been warned that small tanks swing wildly and I keep waiting for it to swing, but maybe it's so lightly stocked and so heavily planted that it's not an issue.Steady as a rock, never more than 20 nitrates, often more like 10. I check it about twice a week but only do a 1-gallon-ish water change every 2-3 weeks when the tannins from the huge piece of mopani wood I put in there months ago make me worry about my plants getting enough light.

36g livebearer tank with many shrimp and, certainly, hundreds of baby fish and snails at this point: I've got so many plants in this bad boy that the nitrates also never seem to get above 20. But the plants and the snails and the livebearers need minerals, baby, and way more than come out of my tap. By the end of the week, any KH I had in my tapwater's been consumed down to 0, and that's after supplementing with wonder shell and crushed coral. So while I want to keep the nitrates up to help my plants thrive and consume all that waste, I still do an 8-gallon water change every week or two to help boost the mineral content and because I'm terrified of waste reaching an intolerable level during the week when I'm not paying as much attention.

So, TL; DR: there are lots of reasons for changing water, and better to small water changes a little too often than to forget to do it entirely for months. So if once a week is what you can remember, that's fine. But know that it may not be necessary to do it that often. Test your water, watch your plants and fish, and you'll figure out what works best for them and you.

[AquaAggie]

So @Keeg  @Fish Folk  @MJV Aquatics  @Maggie and @Kirsten

Thanks for playing along. The take home is that it depends on the tank the inhabitants. I understand @MJV Aquatics as well. It’s a confined system and new  water freshens things up and cleans things up. Fish are always more active etc but at the same time. If it ain’t broke and everyone’s doing well then do what works for you. 

I think that’s the hard part about this hobby. Every tank, every water source, every location is different and going to require different things for different setups. So there is no one right answer.

 

I have a 60g that’s been up and running for a year. 

water parameters:

pH - 7.9
Nitrates - 20
Hardness - 7.5
Nitrite -0
Ammonia - 0
KH/Buffer - 5
Water Temperature - 79
inhabitants:

11 neon tetra (been in tank whole time)
1 pearl gourami (10 months)
M and F apisto caucatoides (6 months)
3 sterbi cories (1 year)
5 khuli loaches (1 year)
1 super red bristlenose pleco (1 year)
2 Bolivian rams (10 months)
1 silver hatchet fish (10 months)
1 pearl scale marble angel (3 months)
4 golden wonder killi (1 month)
nerite snails, MTS, Amani shrimp

I feel like I am on the upper side of stocking limits and have a moderately planted tank. Yet my nitrates are a stable 20 even dosing easy green 1/2 dose now 2-3x a week. I do 50% water change every two weeks just to get some fresh water in and micronutrients but not because anyone is looking sluggish or because the nitrates are bad. Today I dropped to 25% because of time but we will see how it goes. 

[Fish Folk]

sounds beautiful! 

[Hobbit]

I agree with everyone else! Though in actuality I do the complete opposite. 😆 Once my planted 55 gallon had been running for a few months, I went down from 30% water changes weekly to every two weeks. Soon after that water changes started to spread out, and last week I did a 50% water change just because it had been probably three months since the last one. I heard Cory say in a recent live stream that he’s gone three months between water changes and that made me feel better about what I was doing. I have limited energy, so my strategy is to watch the fish and plants closely. If anything seems off, I either test the water or just go ahead and change it.

My water has basically nothing in it—out of the tap it’s pH 6 with GH 1. So changing water doesn’t add micronutrients for my plants unfortunately.

[MJV Aquatics]

You can live in smog, but isn't fresh air better?

Fish can live in pollution, but isn't freshwater better?

[Hobbit]

To expand on my previous answer, I follow @Cory’s philosophy that he outlines in this video: 

I view my tank as an ecosystem and I have lots of plants. Because I’ve done a lot of water testing, I know that my pH is stable at 7.4 and my nitrates never get above 10 no matter how long I go between water changes. (It wasn’t that way at the beginning, of course.) My fish are breeding, I’m raising their fry in that water, and everyone is happy, active, and disease-free. I only change water when I have a reason to—otherwise I just let things be. 

I don’t think there’s anything wrong with changing water often. I just don’t think it’s always necessary. Like @AquaAggie said, 

16 hours ago, AquaAggie said:

If it ain’t broke and everyone’s doing well then do what works for you. 

I think that’s the hard part about this hobby. Every tank, every water source, every location is different and going to require different things for different setups. So there is no one right answer.

 

[lefty o]

depends on the conditions of the aquarium. some require frequent water changes/gravel vac, some can go very long between cleanings.

[Guppysnail]

I worry about things I can’t test for. Stress, breeding, dominance hormones bad bacteria and fungus etc. Lack of something I can’t test for or don’t have that particular kit. I worry about ph/gh/kh swings then putting source water in and swinging it in that direction so try to keep it fresh so it simply matches source water closely.  I like when my all my wet pets are super happy active and that’s always after water changes.  And I simply love to play in water.  I’m a water changer sometimes for no reason at all I just have extra time sometimes I have extra water in buckets I collected the day before for a tank or project and I hate letting it sit more than 24 hours. You name it it’s a good reason to me and my fish love it and forever swim and wiggle adorably against the current of fresh water. I’m not the scientist type so don’t have charts and stuff but I’m consistent with never missing. All my fish have always been super healthy once in a forever home tank. I have very minimal what I consider a healthy amount of algae so I just do what I’ve always done and keep it fresh. 

[MJV Aquatics]

The sad truth is that fish can live, or rather survive, in poor quality water. This seems to give some hobbyists a 'license' to skimp on routine partial water changes. In nature fresh water is constantly renewed by rains and snow melt. Just look at all the creeks, streams, and rivers etc. that flow endlessly on the way to the ocean...And yes, there are some exceptions but I would suggest that the water quality is lower in those exceptions. Having an aquarium with infrequent partial water changes is like a small animal cage that rarely if ever gets cleaned - 'stuff' builds up.

A well established tank with lots of plants can go longer and/or have a lower volume partial water changes...but (being redundant here) generally speaking, there's no such thing as too much fresh water.

Too many times on forums like this we see hobbyists brag about rarely or never doing partial water changes. They claim that their fish are fine...and even breed. Some say their fish live an average life span of 2-3 years...when the average life span of tropical fish is 10-15 years. Then there's the hobbyist that can't figure out why his old fish 'are just fine' but any newly added fish die in a day or two. S/he blames the fish store for poor quality fish rather than the poor quality of the water in his/her aquarium.

So up to a point, aquatic life can survive in poor quality water, but it rarely thrives there. Fresh water is always better than polluted water. :-)

[Odd Duck]

@MJV Aquatics  Hear, hear!  Very well said.

When I rescued my pair of adult Jack Dempseys, their tank looked like the water hadn’t been changed in months and since the owner didn’t even have a gravel vac there was soooooooo much mulm built up I couldn’t even tell what color the gravel or tank ornaments were at first.

When they got cleaned gravel and fresh water, they bred for their first time only 5 weeks after I got them.

I’m not saying that everyone’s tank is that way that doesn’t do frequent/regular water changes.  I think most that talk about infrequent changes have heavily planted, lightly stocked tanks, not the *no plants, poorly filtered, hot mess* that I was confronted with when I agreed to take over the care for these poor Jacks.

I think with very light stocking, loads of plants, and good water going in initially, and topping off with RODI, it’s entirely possible to do minimal water changes.  But there are sooooo many things we just can’t measure in our tanks.  Why should we push our fish to tolerate what may be a massive soup of hormones or other, unmeasurable chemicals to them, that may have adverse effects we know nothing about?

Jumping off my soapbox now.  Hopefully just a little more food for thought for anyone interested.

[KentFishFanUK]

On 7/23/2021 at 2:54 PM, MJV Aquatics said:

The sad truth is that fish can live, or rather survive, in poor quality water. This seems to give some hobbyists a 'license' to skimp on routine partial water changes. In nature fresh water is constantly renewed by rains and snow melt. Just look at all the creeks, streams, and rivers etc. that flow endlessly on the way to the ocean...And yes, there are some exceptions but I would suggest that the water quality is lower in those exceptions. Having an aquarium with infrequent partial water changes is like a small animal cage that rarely if ever gets cleaned - 'stuff' builds up.

A well established tank with lots of plants can go longer and/or have a lower volume partial water changes...but (being redundant here) generally speaking, there's no such thing as too much fresh water.

Too many times on forums like this we see hobbyists brag about rarely or never doing partial water changes. They claim that their fish are fine...and even breed. Some say their fish live an average life span of 2-3 years...when the average life span of tropical fish is 10-15 years. Then there's the hobbyist that can't figure out why his old fish 'are just fine' but any newly added fish die in a day or two. S/he blames the fish store for poor quality fish rather than the poor quality of the water in his/her aquarium.

So up to a point, aquatic life can survive in poor quality water, but it rarely thrives there. Fresh water is always better than polluted water. 🙂

I think I am going to have to play devils advocate here as I'm not sure I entirely agree with all your points. With all due respect of course, you are far more experienced than myself! 

First you mention about water in the wild being constantly renewed. Aren't some bodies of water simply topped up but otherwise not really flowing as such? Besides, in many environments these rain water etc 'renewals' actually hugely increase water turbidity and presumably mean a lower water quality in some respects, temporarily at least. I would also guess that these renewals actually excite fish with the prospect of more food arriving with it and that is possibly why we see increased activity etc. 

Secondly what even is 'fresh' water? Most of us will be using municipal water which we simply don't know the exact chemical make up of. My tap water, for example, comes out around 40-50 ppm of nitrates (50 being the legal UK limit apparently) yet my planted tank always reads around 20-30 ppm so in that regard is actually cleaner. I get that that's only one of the half dozen or so parameters we test for the bazillion others we don't test but still I'm sure the same could possibly be said for heavy metals or bacteria and who knows what else too. I know we could use RO water and add in the minerals etc we need but even then do we really know nothing beneficial at all is missing? Or nothing harmful has made its way in? Kind of leads to my next point - 

You say there's no such thing as too much fresh water, too many water changes etc but couldn't it be argued that sometimes a build up of 'stuff' could help fish build strength or higher tolerances to such fluctuations in parameters? Or when breeding help the gene pool stay 'hardier?' As per natural selection and all that. I mean humans like oxygen and dislike virus' and pollutants but I'm pretty sure I can be confident in saying raising human babies in a bubble only ever breathing purified air would not be conducive to building the individuals immune system or the populations hardiness. 

My last thought which might be less relevant (or more stupid but I'm enjoying my uneducated musings on the subject so bare with me) - many of our traditional food preservation methods boil down to allowing a strong colony of harmless bacteria to thrive on the food and as such out compete harmful bacteria so as to keep the food safe for us to eat. In a thriving and balanced ecosystem this could potentially be playing a role in a similar way (similar to a balanced tank having less algae issues) but by messing with it could lead to an imbalance allowing a harmful bacteria to multiply and threaten a fish with sickness of some sort. 

I think your method is surely the 'safe bet' answer, as with so many variables to consider it is impossible to factor everything in to come to the perfect conclusion, and it is the tried and tested method and general wisdom/consensus answer to the question after all. However I don't think it is nearly as black and white as you imply. 

 

Does their happen to be any freshwater biologists or hydrologists or microbiologists around to explain why everything I just typed is nonsense? 😅

[Ben_RF]

Check out this video by this amazing fishtuber, our @Irene!
 

 

[MJV Aquatics]

On 7/24/2021 at 10:26 AM, KentFishFanUK said:

I think I am going to have to play devils advocate here as I'm not sure I entirely agree with all your points. With all due respect of course, you are far more experienced than myself! 

First you mention about water in the wild being constantly renewed. Aren't some bodies of water simply topped up but otherwise not really flowing as such? Besides, in many environments these rain water etc 'renewals' actually hugely increase water turbidity and presumably mean a lower water quality in some respects, temporarily at least. I would also guess that these renewals actually excite fish with the prospect of more food arriving with it and that is possibly why we see increased activity etc. 

Secondly what even is 'fresh' water? Most of us will be using municipal water which we simply don't know the exact chemical make up of. My tap water, for example, comes out around 40-50 ppm of nitrates (50 being the legal UK limit apparently) yet my planted tank always reads around 20-30 ppm so in that regard is actually cleaner. I get that that's only one of the half dozen or so parameters we test for the bazillion others we don't test but still I'm sure the same could possibly be said for heavy metals or bacteria and who knows what else too. I know we could use RO water and add in the minerals etc we need but even then do we really know nothing beneficial at all is missing? Or nothing harmful has made its way in? Kind of leads to my next point - 

You say there's no such thing as too much fresh water, too many water changes etc but couldn't it be argued that sometimes a build up of 'stuff' could help fish build strength or higher tolerances to such fluctuations in parameters? Or when breeding help the gene pool stay 'hardier?' As per natural selection and all that. I mean humans like oxygen and dislike virus' and pollutants but I'm pretty sure I can be confident in saying raising human babies in a bubble only ever breathing purified air would not be conducive to building the individuals immune system or the populations hardiness. 

My last thought which might be less relevant (or more stupid but I'm enjoying my uneducated musings on the subject so bare with me) - many of our traditional food preservation methods boil down to allowing a strong colony of harmless bacteria to thrive on the food and as such out compete harmful bacteria so as to keep the food safe for us to eat. In a thriving and balanced ecosystem this could potentially be playing a role in a similar way (similar to a balanced tank having less algae issues) but by messing with it could lead to an imbalance allowing a harmful bacteria to multiply and threaten a fish with sickness of some sort. 

I think your method is surely the 'safe bet' answer, as with so many variables to consider it is impossible to factor everything in to come to the perfect conclusion, and it is the tried and tested method and general wisdom/consensus answer to the question after all. However I don't think it is nearly as black and white as you imply. 

 

Does their happen to be any freshwater biologists or hydrologists or microbiologists around to explain why everything I just typed is nonsense? 😅

 

1 - Yes, there are some bodies of water not fed by streams or rivers (but not the case for most wild tropical fish). Many of these are spring fed and there are sky ponds that collect rain water, most of which have overflows.  Most stagnant pools of water are often foul and the quality of those waters is probably less than waters that are constantly refreshed, Many contain little or no aquatic life.... And 'muddy' water, although not clear, is just not the same as polluted water. During the rainy season, many bodies of water overflow creating ponds in ditches. Sadly the life trapped there survives only as long as the water does.

2- More and more we see high nitrates in source drinking water, especially in agricultural areas with farmland runoff where animal waste and/or high nitrogen fertilizers are used. I've written volumes about the nitrates in my well water. I tend to believe (but of course can't prove) that nitrates in source water is not as harmful as tank generated nitrates. Perhaps because tank generated nitrates also contain many other pollutants we simply can't measure.

3. The fact is that a partial water change does not remove all bacteria, merely reduces the pollution by dilution. Fish food and fish/plant waste build up in the glass cage and plants and bacteria can only do so much to purify and filters merely trap detritus where it continues to decompose and pollute the water - oh the water looks cleaner, but it is not more pure. The only way to really maintain a somewhat stable water chemistry in an aquarium is with routine partial water changes to dilute the pollution and replenish valuable necessary minerals.

I will admit that I am still learning but I base the above on over 50 years in the hobby with some lessons learned the hard way. 🙂

Edited July 24, 2021 by MJV Aquatics
update

[KentFishFanUK]

On 7/24/2021 at 3:59 PM, Ben_RF said:

Check out this video by this amazing fishtuber, our @Irene!
 

 

Love Irene! Her videos are so watchable I think I've watched them all by now lol

[HH Morant]

I think water changes are generally helpful. I don't think you lose any beneficial bacteria (the video mentions that as a possibility). I also don't think there is anything wrong with a water change greater than 50% (the guideline in the video).

On the other hand, I think the danger of nitrates - the main reason for water changes- is overstated by most in the aquarist community. I am not aware of any research that supports a 40 ppm nitrate target. I don't count statements on the labels of dechlorinators, because the manufacturers make more money (a lot more) if you aim for 40 ppm, or 30 or 20, than if you think the nitrate level is not really very important.

My nitrates are often in the 40-80 range, and I do not believe that hurts the fish. I sometimes do 67% water changes every 2 weeks, sometimes every three weeks. I change the water in my mom's aquarium when I visit her (she cannot do it), which is every couple of months or so. The nitrate levels in her aquarium are often over 100 ppm, but her fish are fine.

I am not aware of any research that supports the assertion that nitrates in the 100 range decreases the life expectancy of fish. Several scientific studies are discussed in an article entitled "Nitrate in Depth" on the site aquariumscience.org. 

I know most hobbyists will disagree with me, and certainly there is nothing wrong with keeping your nitrates at 20 ppm if that is what you want to do. But I think this is the lore of fishkeeping and not necessarily scientific.

[KentFishFanUK]

On 7/24/2021 at 4:49 PM, MJV Aquatics said:

1 - Yes, there are some bodies of water not fed by streams or rivers (but not the case for most wild tropical fish). Many of these are spring fed and there are sky ponds that collect rain water, most of which have overflows.  Most stagnant pools of water are often foul and the quality of those waters is probably less than waters that are constantly refreshed, Many contain little or no aquatic life.... And 'muddy' water, although not clear, is just not the same as polluted water. During the rainy season, many bodies of water overflow creating ponds in ditches. Sadly the life trapped there survives only as long as the water does.

2- More and more we see high nitrates in source drinking water, especially in agricultural areas with farmland runoff where animal waste and/or high nitrogen fertilizers are used. I've written volumes about the nitrates in my well water. I tend to believe (but of course can't prove) that nitrates in source water is not as harmful as tank generated nitrates. Perhaps because tank generated nitrates also contain many other pollutants we simply can't measure.

3. The fact is that a partial water change does not remove all bacteria, merely reduces the pollution by dilution. Fish food and fish/plant waste build up in the glass cage and plants and bacteria can only do so much to purify and filters merely trap detritus where it continues to decompose and pollute the water - oh the water looks cleaner, but it is not more pure. The only way to really maintain a somewhat stable water chemistry in an aquarium is with routine partial water changes to dilute the pollution and replenish valuable necessary minerals.

I will admit that I am still learning but I base the above on over 50 years in the hobby with some lessons learned the hard way. 🙂

1. Fair enough! I had assumed the muddy water would also increase the dissolved organics and pollutants from the particles that have been stirred up or from run off etc but only because it makes sense to me not because I've read any studies or anything! 

2. There is a lot of farmland in my part of the country so thats probably why the nitrates are so high. Also interesting hypothesis! I'd love to know if you are right there, would be pertinent info for the whole hobby to know. My assumption would have been that tank generated nitrates are, if anything, less harmful than those from source water being that it's how it would occur in a natural environment as part of a natural cycle without agriculture etc interfering, but again that's not very scientific of me just what seems to make sense in my brain. 

3. True it wouldn't remove all water born bacteria (or yeasts or other microorganisms) but my hypothesis is that it could remove enough that it potentially allows non favourable ones the chance to establish in their place. I'd love to know the statistics of say, the occurrence of ich in very regular large water changed tanks compared to walstad method tanks (so opposite ends of the spectrum). Anyone know of any such studies? After all many of the pollutants we think about can be removed from tanks in other ways not just water changes - trimming plants, squeezing out sponge filters, removing algae, removing snails and probably other ways that I can't think of right now. 

But yes either way you can't argue with 50 years experience! Was just pointing out the fact that I don't think people's successes with few or even zero water changes can be so easily dismissed. Of course they might not be enough to go as far as recommending zero water changes, especially to a beginner but worth consideration in the hobby nonetheless (maybe even worth writing books about 😂)

Thanks for replying to my long winded posts! I don't get out much... haha

[KentFishFanUK]

On 7/24/2021 at 4:53 PM, HH Morant said:

I think water changes are generally helpful. I don't think you lose any beneficial bacteria (the video mentions that as a possibility). I also don't think there is anything wrong with a water change greater than 50% (the guideline in the video).

On the other hand, I think the danger of nitrates - the main reason for water changes- is overstated by most in the aquarist community. I am not aware of any research that supports a 40 ppm nitrate target. I don't count statements on the labels of dechlorinators, because the manufacturers make more money (a lot more) if you aim for 40 ppm, or 30 or 20, than if you think the nitrate level is not really very important.

My nitrates are often in the 40-80 range, and I do not believe that hurts the fish. I sometimes do 67% water changes every 2 weeks, sometimes every three weeks. I change the water in my mom's aquarium when I visit her (she cannot do it), which is every couple of months or so. The nitrate levels in her aquarium are often over 100 ppm, but her fish are fine.

I am not aware of any research that supports the assertion that nitrates in the 100 range decreases the life expectancy of fish. Several scientific studies are discussed in an article entitled "Nitrate in Depth" on the site aquariumscience.org. 

I know most hobbyists will disagree with me, and certainly there is nothing wrong with keeping your nitrates at 20 ppm if that is what you want to do. But I think this is the lore of fishkeeping and not necessarily scientific.

Not sure if you were replying to me but to clarify I didn't mean water changes would remove some of the beneficial bacteria as in nitrifying bacteria but other beneficial bacterias, or simply non harmful ones that establish and thus help keep out harmful ones (which I guess would make them beneficial too but not in the way we normally mean it). 

But yes I'm not sure I've ever heard where the whole >40 ppm nitrates bad, <40 ppm nitrates good thing ever came from. 

[Hobbit]

I think it’s also worth adding another factor to this discussion: how often do you clean your filter? I have heard some knowledgeable people claim that this helps remove harmful material that we can’t necessarily test for. I don’t change water nearly as frequently as @MJV Aquatics would like me to 😅 but I rinse out my filter much more often. Of course, one should do both. But I wonder if going heavy on one might compensate (in some ways) for going light on the other.

[KentFishFanUK]

On 7/24/2021 at 5:41 PM, Hobbit said:

I think it’s also worth adding another factor to this discussion: how often do you clean your filter? I have heard some knowledgeable people claim that this helps remove harmful material that we can’t necessarily test for. I don’t change water nearly as frequently as @MJV Aquatics would like me to 😅 but I rinse out my filter much more often. Of course, one should do both. But I wonder if going heavy on one might compensate (in some ways) for going light on the other.

Good point! I have only been doing small infrequent water changes due to the high nitrates in my tap water, but I have been cleaning out my filter sponge. In fact the amount of tank water I use to squeeze out the sponge is the amount I replace and don't really do any water changes on top of that. Though to be fair I've only been doing even that like once every two weeks (maybe less 😅) so maybe that's not enough whichever way you look at it! Parameters I can test for with the API master test kit are fine though (better in fact). That reminds me I really need to get a GH/KH test kit too. 

[laritheloud]

I don't have any fact-based reasoning to back up what I do, but I change all my tanks at around 30 to 50% every week, including wiping down the inside and outside of the glass and rinsing/cleaning my filters. The fish always seem to perk up with a water change and it often triggers spawning behaviors in my tetra. I like to create a habit/routine and stick with it.

Caveat: I do have a legit OCD diagnosis, and a set routine and predictability is very helpful in maintaining my tanks without caving in to an impulse of overdoing it. So this is what works for me.