PWCs with a stable tank

[Martin]

Good morning guys!

Just wanted to solicit for opinions regarding the need for PWCs if your tank parameters hold stable in a moderately planted tank.  Week after week, my parameters have been unchanged, but I did 20% changes out of habit, however, for the past 3 weeks, I've forgone changes as the parameters remain unchanged regardless.  Everything seems happy and healthy.

I've read some opinions online equating fresh water for the aquarium to fresh air to us as humans, but I've also seen opinions of "it ain't broke, don't fix it."  Any thoughts?  I'm leaning towards just reducing the frequency of my PWCs.  As always, thank you wonderful people in advance!

[Isaac M]

Hi @Martin, personally I try to tinker as little as possible with my aquariums. I would do less water changes if the parameters are holding steady (nitrates are not too high). Every once in awhile (3 months or so) I will do a partial water change to replenish the mineral content in the water for my aquariums. It is mostly to prevent old tank syndrome(watch your gh & kh) but honestly, I could probably go a lot longer than 3 months. That is my take on it. 

[Martin]

Thanks Isaac!  My nitrates are actually close to zero, which is kind of why I wanted to reduce my interference (I usually do a little gravel vac'ing when I PWC).  Given my nitrates are almost non-existent, I figured the some of the fish/food waste might be a good thing to leave around for the benefit of the plants.  Nitrites are zero.

[Isaac M]

No problem @Martin, how are your plants doing with that low of nitrates? Are they showing any nitrogen deficiencies? Typically for plants you want to have 20ppm nitrates or even higher. I am assuming you have plants that prefer fertilizer from the water column but I could be wrong here as you may be using an enriched substrate with heavy root feeder plants. 
 

Yeah I do not gravel vac my planted aquariums for the same reason. I leave all the waste there for the plants to consume. Mulm is a great thing to have in a seasoned aquarium. 

[Jollypop4321]

Recently there was a couple videos posted regarding the frequency of water changes. One was by Steenfont aquatics and @Cory addressed this issue on his last video as well.   Maybe these videos will give you more insight?
 

[lefty o]

the weekly partial water change thing is way over done imo.

[Martin]

@Isaac M, I haven't noticed any nitrogen deficiency related issues in the majority of my plants, though I did lose my bacopa caroliniana about a month ago.  Based on the signs it was showing (browning/rotting of older leaves and the stem), that may have been the culprit.  My aponogeton has slowed its growth bigtime, but consensus on that one is that it is likely entering its dormant phase.  All my other plants (amazon sword, 2x cryptos, java fern) seem to be healthy.  I've been dosing with Seachem Flourish (in addition to EZ Green and root tabs), but the nitrates always remain low.  Maybe I need to consider dosing a little more frequently.

Yeah, I've dialed back the gravel vac'ing a lot.  It helps that I use Fluval Stratum substrate, which is jet black, so I don't see all the build-up anyway.  Also, given the plants are everywhere, it's hard to vac that tank anyhow.

[eatyourpeas]

I think that skipping your PWC can lead to a build up of TDS in your tank. Unfortunately, when you do a water change that is on the large side, it can throw your parameters and shock the livestock and by the time you notice, it is too late. I do not vacuum the substrate to allow for critter waste to provide nutrients for the plants, but do 60% weekly WC.

Having said that, every tank is different 🙂

[Martin]

Thanks @eatyourpeas, sorry I'm not up on all the lingo, TDS?  Something-something syndrome?

[eatyourpeas]

1 minute ago, Martin said:

Thanks @eatyourpeas, sorry I'm not up on all the lingo, TDS?  Something-something syndrome?

Total dissolved solids. 🙂

[Isaac M]

@Martin Aponogeton feed a lot from their bulb so they will do well without water column fertilizer, given that you have fluval stratum, the aponogeton will feed itself from the substrate so it can go dormant and come back as strong as before. Amazon swords and crypts are mostly root feeders so they do not need much out of the water. The java fern definitely prefers water column fertilizer but grows so slowly it may not be needed. I would not dose more frequently unless you have stem plants or other plants that do well with fertilizer in the water column. 

As far as TDS, I personally do not test for it as I do not really get anything from it. It is a number telling us the total dissolved solids in the water but does not tell us what it is. Even while in college, I had labs where we tested for tds in water samples and then added flocculants to make the water less turbid/ have less tds. It never told us what the solids were though.

Assuming you have plants, which would be likely the only way to keep on having low nitrates week by week without a water change, they will be utilizing minerals in the water also to grow. If anything, your TDS may actually go down because of this. That is why I recommend to watch your kH and gH. You do not want it to dip down too much as you can have pH dip and/ or stunted growth (& other issues) in the inhabitants. This will generally take a long time to happen but still something to keep in mind. 

I know this may be a lot of information to take in all at once. I just wanted to make sure I explained my thought process. To simplify, I would recommend this:

Test your nitrates every week. Do a 20%-30% water change when the nitrates go over 40ppm. If it takes longer than a month for this to happen, test your gH and kH. Assuming you know your baseline values (whatever the gH and kH of the tap water is), you can check if they are dipping. gH should typically be over 4dgh and kH should be over 2dkh. Do a water change when you begin to see these numbers trending downwards. 

I hope this helps! Aquarium co-op has a lot of great videos and articles on this topic as well if you want to look more into it. 

[Patrick_G]

Back in the day before planted tanks were the norm we changed water to control the buildup of Nitrates. Someone correct me if I’m wrong but plants have really changed the equation.  Now a highly planted, lightly stocked tank can go for a long time between water changes. 

[Martin]

Thanks guys!  @Isaac M, thanks for all the great information!  I've been vigilant about testing my water.  I'm actually quite surprised at how my parameters haven't budged at all.  I just got done doing a small PWC just because its been about a month, and because I needed to change the scape a little bit to accommodate a couple of incoming new plants.  I had opted to use small Wondershells since my water is somewhat soft.  I was really surprised as the whole darn shell dissolved in one day.  Strangely, GH hasn't dropped, even with my prior PWCs... not sure what's up with that.  KH has been very difficult to raise.  It has always been low, regardless of dosing with whatever that respective Seachem product is called (sorry, they have WAY too many to remember).  In any case, I'll keep an eye on everything and in general, I probably will be dropping the frequency of the water changes to maybe once every 3-4 weeks assuming no major changes.