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low KH question from a newbie


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Hello, 

I'm looking for help understanding what super low KH means and how a PH crash works. I started my first tank (29G) two weeks ago. Initial readings for PH/ KH were about 7/4, but would drop to 6/0 over the course of a couple days without a water change (there's driftwood and fluval stratum in the tank). The GH would remain around 5. I'd like to keep Honey Gourami and Kuhli Loaches which I've read do well in softer water- but the PH crash thing worries me.  It seems like any alternative to raising the KH also raises the PH and if PH gets too high, then the parameters aren't right for the gourami and kuhli loaches. 
 
I've read that KH is a buffer for PH but I don't completely understand what this means- particularly in relation to a PH crash. And does a higher KH mean a higher PH or is that only if you're taking active steps to raise one or the other? (such as a buffer). And is it possible to raise KH without raising PH? What causes a PH crash exactly? 
 
When my readings were showing KH at 0 and PH dropping I panic bought crushed coral and have since bought Alkaline Buffer (this was before I landed on Honey Gouramis and Kuhli Loaches as my fish of choice). I also got droplet kits for PH and KH/GH (I had been using a strip kit). I put a handful or so of crushed coral into my HOB. I have not yet opened the Alkaline Buffer. 
 
The handful of crushed coral kept my PH levels consistent at 7, KH at 2, and GH at 5 for about a week and through 2 water changes (one about 50% on about 70%). However, after another 70% water change and adding some plants yesterday, it read PH 7.2, KH 3, and GH 6, which is getting out of the range of the fish I'd like to keep. The levels are now back to 7/2/5. 
 
Am I messing around with the tank too much? Should I take out the crushed coral and see where the parameters land without any boosts? Or should I try the Alkaline Buffer? Do I need to give up on softer water fish to raise my KH and thus my PH? Any kind of guidance would be much appreciated. 
 
-Chris
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Baking soda is a cheap and effective kh puffer. Epsom salts are a good gh buffer. I am surprised that your ph and kh drops so much, though 4dkh is a bit on the lower side. What happens if you just leave a bucket of your tap water out for 24 or 48 hours? CO2 in the air of your home can actually decrease aquarium ph over time as well. You can try removing the driftwood from the tank and boiling it in water for an hour or two, changing the water occasionally, to get most of the tannins out of it.

It's best, as you probably know, not to chase numbers. Most of the fish that have been in the hobby for a while (not wild caught, but captive bred) are fairly hardy and adapt to a wide range of ph and hardness.

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Both Honey Gourami's and Kuhlis can handle a fairly wide range as long as you have some consistency, I would stick with whatever you have coming out of the tap to begin with and smaller water changes so you don't get those big swings in numbers, like ererer said chasing numbers can be a real rabbit hole.  Once you see plant growth and know your tank is good and cycled then add fish and see how they do.

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I can try leaving some water out and test it over a couple days to see what happens. I know that the stratum and driftwood can lower PH so I've mostly been attributing it to that. I did boil the driftwood for four hours and then soak it for a month before filling up the tank so it's not really leaching any tannins. 

Not chasing numbers makes a lot of sense. Being new I know I'm way too reactive. The PH crash thing just freaks me out. 

Thanks! 

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Yeah, the "buffering" is like a shield against "acid attacks", too low and it will wear out and pH may crash. If your tap water is at 4 dKH, regular water changes would keep the shield energized. I think. Crushed coral would also help. But If I understand it correctly, fluval stratum lowers pH, and must eat away the shield to do so. Maybe you are fighting a battle you cannot win here?

Edited by darkG
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Just a quick rundown of PH, GH, and Kh. PH basically is telling you how acidic or how basic your water is. PH 7.0 is neutral, lower numbers mean its acidic or soft water, higher numbers mean it basic or hard water. Water is sometimes referred to as the universal solvent. Water dissolves solids like calcium, or magnesium for example. When it does those dissolved solids give you your GH. The higher the GH number the more dissolved solids there are and vice versa. If water has a low general hardness it will leach those minerals out of everything it touches. If it is fully saturated it wont leach out those minerals. Sorta like sugar in tea, just a bit of sugar mixed in tea will dissolve, if you put too much sugar in tea, tho some of it will dissolve, you can still see sugar granules swirling at the bottom of the glass. Your KH is your carbonate hardness. Simply put its what your acidic water will begin to dissolve first. The more basic your water is, the longer your KH will last. The more acidic your water is the faster your KH will drop. After all your carbonates and bicarbonates are eaten by the acidity of the water meaning KH = 0. Your buffer so to speak is now gone. As the carbonates and bicarbonates get eaten by acid it cancels out that acidity. With nothing left to calm down the acid ( like when you run out of tums tablets) your water will continue to get more and more acidic meaning your PH  will get lower and lower. Thats why low KH crashes your PH. 

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Thanks Will Billy and Dark G. I had a basic understanding, but the analogies definitely help. 

I guess what I don't understand is, my PH is fairly high out of the tap. I just measured it around a 7.6. But the KH is still only 4. GH was 9. How can the KH be so low with the PH being higher? 

The PH being so high explains why the numbers jumped up after the major water change. I guess to proceed I can only do very minor, and more regular water changes to not risk a crash? Or can crashes occur from other things too? 

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4 minutes ago, cclements said:

How can the KH be so low with the PH being higher? 

A few factors to consider for this question. #1 it depends on your source water. My tap water from my municipality is quite similar to yours. It all depends on what you are starting with. 4dKH is a little low but not too bad considering your PH is a little high. That means your KH is doing its job keeping your PH up. As your KH does what its supposed to do it is used up which is why it makes sense that your KH is low, its buffering your PH. 
 

12 minutes ago, cclements said:

I guess to proceed I can only do very minor, and more regular water changes to not risk a crash? Or can crashes occur from other things too? 

The reason why tannins, fish activities, bacterial activities, plant activities, a.k.a. eating, drinking, breathing, pooping, and peeing, all reduce your KH over time is because they are putting more and more acidic substances in your water, and conversely they are removing ever more minerals from the water. Both activities adding acids, and removing bases from the water column are lowering your PH causing KH to be eaten ever faster which maintains your PH level until its all gone. Some people with good quality water for the aquarium hobby can maintain KH through simple water changes. The rest of us have to add minerals to adjust our chemistries like seachem equilibrium for GH or seachem alkaline buffer for KH. Some people have water chemistries so out of whack that have to add RO or distilled water to cut back on both and then boost one or the other. I think in your case as you are somewhat new to this and i dont know your bioload, i would just test and monitor to get a feel of how much and how often you should perform water changes. It just takes time, you will get to know your water and what it needs and before long you will be doing it almost automatically without any thought. Good luck luck to you and i hope you enjoy this wonderful hobby. Any more questions please feel free to ask. 

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37 minutes ago, Will Billy said:

 The rest of us have to add minerals to adjust our chemistries like seachem equilibrium for GH or seachem alkaline buffer for KH. Some people have water chemistries so out of whack that have to add RO or distilled water to cut back on both and then boost one or the other. I think in your case as you are somewhat new to this and i dont know your bioload, i would just test and monitor to get a feel of how much and how often you should perform water changes. It just takes time, you will get to know your water and what it needs and before long you will be doing it almost automatically without any thought. 

This is hugely helpful and reassuring, thank you. 

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I am fairly new to fish-keeping and having stable water parameters was one saving grace while fighting other issues in my cichlid tank.  If I’d had to battle my water on top of the rest, I probably would have given up. 
 

I don’t have any advice to give you, but do have a question... why would you be doing 50% and 70% water changes after only 2 weeks?  Especially on an empty tank?

The most I’ve ever changed out at once was about 25% when doing weekly changes towards the beginning stages.  I currently do closer to 15-20% every 10-14 days.

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Its not entirely empty. I've gradually been filling it with plants, attempting to run the fishless, planted cycle I found on aquarium coops youtube channel. Unfortunately I ordered plants at the worst possible time and they got caught up in the delays. Because of this I've been planting in stints and the health of some of the plants haven't always been great (the order from AC came in surprisingly well tho!). Cory's video didn't mention water changes and I knew plants consumed ammonia and nitrates eventually so I didn't think I needed to do them. But when my plants started melting heavily (including ones that came in in relatively good shape), I did more research and found that ammonia can burn plants if they're not set up to handle the load or weren't as hardy, which some weren't.  Knowing I had dying plants due and substrate contributing to the ammonia in the tank, in addition to seeing the KH drop to about 0, I started doing water changes. 

I did about a 30 percent the first time kh dropped to 0. The next one was the first 70 percent, after I read about ammonia burning plants. The 50 was a few days after. And then the next 70 percent I did mostly because I got more plants in, including moss which I wanted to secure more easily to driftwood toward the bottom of the tank. 

I wouldn't be surprised at all of I'm over doing it. 

 

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17 minutes ago, cclements said:

Its not entirely empty. I've gradually been filling it with plants, attempting to run the fishless, planted cycle I found on aquarium coops youtube channel. Unfortunately I ordered plants at the worst possible time and they got caught up in the delays. Because of this I've been planting in stints and the health of some of the plants haven't always been great (the order from AC came in surprisingly well tho!). Cory's video didn't mention water changes and I knew plants consumed ammonia and nitrates eventually so I didn't think I needed to do them. But when my plants started melting heavily (including ones that came in in relatively good shape), I did more research and found that ammonia can burn plants if they're not set up to handle the load or weren't as hardy, which some weren't.  Knowing I had dying plants due and substrate contributing to the ammonia in the tank, in addition to seeing the KH drop to about 0, I started doing water changes. 

I did about a 30 percent the first time kh dropped to 0. The next one was the first 70 percent, after I read about ammonia burning plants. The 50 was a few days after. And then the next 70 percent I did mostly because I got more plants in, including moss which I wanted to secure more easily to driftwood toward the bottom of the tank. 

I wouldn't be surprised at all of I'm over doing it. 

 

I don’t have live plants, so I have no knowledge there.  I was just curious. Good luck!  I hope you figure it out!
 

 

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Its all good @cclements, we all get nervous when we try new things. Its normal for plants to melt a bit when first planted, they will grow back. Typically once your tank has fully cycled and the beneficial bacteria have taken over the main task of reducing ammonia and nitrites, Most people do between 15-20% water changes a week and maybe a 30-50% once a month. A lot of that depends on not only your bioload, but also your tank inhabitants. Me for example, My display tank has turned into a guppy grow out tank with an ever expanding army of guppy fry and 2 large dojo loaches that are quite honestly glutenous piggies. My tank gets 30-50% water changes a week depending on nitrate levels. I have a huge bioload with fish that can handle large water changes. Most people that keep shrimp for example do smaller water changes as shrimp dont do well with big water changes like i end up doing with my tank. You will get the hang of it, no one set in stone method is right for everybody. Someone with a Walstad tank with few fish will definitely do far less water changes than my heavy bio load guppy farm i have going on. Like i said you will grow to know your water with experience. 

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Sorry for piggybacking on the original poster but I have a very similar question.

I have three tanks; a 72, 36 and 20 gallon tanks. The 72 runs a KH of 3 GH 9, 36 runs KH 4 GH 10, the 20 gallon KH 2 GH 10.

I would love to have them all around 5 or 6 KH.

The GH I'm fine with. The 36 and 72 keep PH around 6.8 - 7.0. The problem I'm having is with the 20 gallon, It's my bare bottom quarantine tank. The PH keeps dropping below 6, I assuming because of the low KH. 

How do I raise the KH in that tank without raising the GH? The other two tanks how do I raise the KH without raising the PH and GH?

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1 hour ago, Medkow74 said:

Sorry for piggybacking on the original poster but I have a very similar question.

I have three tanks; a 72, 36 and 20 gallon tanks. The 72 runs a KH of 3 GH 9, 36 runs KH 4 GH 10, the 20 gallon KH 2 GH 10.

I would love to have them all around 5 or 6 KH.

The GH I'm fine with. The 36 and 72 keep PH around 6.8 - 7.0. The problem I'm having is with the 20 gallon, It's my bare bottom quarantine tank. The PH keeps dropping below 6, I assuming because of the low KH. 

How do I raise the KH in that tank without raising the GH? The other two tanks how do I raise the KH without raising the PH and GH?

There's several ways to, but I like using Potassium Carbonate (K2CO3). It dissolves instantly and super cheap.

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On 3/10/2021 at 3:05 PM, cclements said:

Thanks Will Billy and Dark G. I had a basic understanding, but the analogies definitely help. 

I guess what I don't understand is, my PH is fairly high out of the tap. I just measured it around a 7.6. But the KH is still only 4. GH was 9. How can the KH be so low with the PH being higher? 

The PH being so high explains why the numbers jumped up after the major water change. I guess to proceed I can only do very minor, and more regular water changes to not risk a crash? Or can crashes occur from other things too? 

That's not too far off what I'd expect my pH to be at that KH in a low tech tank. But to answer the question, tap water has a bit of dissolved gases in it. CO²  and O² for sure. As they gass off or equalize to the atmosphere, the pH fluctuates. After some time, your numbers will make more sense.

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