My freshwater tank levels won’t go down and it’s killing my fish

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Aquarium Advice Newbie
May 30, 2024
I recently changed the rocks in my tank from rainbow ones to black and purples ones, and while doing so, I did a partial water change to clear up some of the access residue from the rocks.

That next morning I noticed that my catfish (Cory catfish and albino catfish) were staying at the bottom of the tank and seemed lethargic, which I thought was weird because my platy and my Mollies all seemed fine. I noticed that my Cory catfish eyes were white so I immediately assumed I had an ammonia spike in my tank. I checked my levels and my nitrate was 160, nitrite was 3.0, hardness was 75, KH was 300, and ph was 7.8

I did a partial water change (25%), used Prime to condition it before putting it in the tank, and I also put Aquarian ammonia remover. I waited a few hours and checked levels again. Everything was the same except the ph was about 8. To try and lower ph I used half a tablet of PH balance. Checked levels again and PH was about 8.4. I did some research online and it said that high KH can cause high PH so I did a 25% water change and instead of using tap water (conditioned of course) I used distilled water. I checked levels again and everything stayed the exact same. I did more research and found that using Tetra easybalance should help with nitrate, hardness, alkalinity, and ph. Waited a few hours to check levels then still NO CHANGE.

My Cory catfish died, one of my snails died, my albino catfish is still lethargic at the bottom of the tank not eating, and now one of my Mollies stopped eating is developing symptoms of swim bladder.

I have no idea what to do and I’m afraid that I’m going to lose my whole tank. I seriously could use help. Anything helps please


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What is the ammonia test result?

When you say rocks, do you mean substrate (gravel) or large pieces of rocks in your aquascape?

Have you been regularly testing the water when you didnt have problems? If so, whats a typical set of test results?

It looks like changing whatever you changed did 2 things.

1. Removed some of the microbes responsible for you cycle. It will take some time for your cycle to re-establish. In the meantime you need to do water changes to keep things safe. Test daily, take your ammonia and nitrite and add then together. Add them together. If the combined total is more than 0.5ppm combined change enough water to bring it below that 0.5ppm combined target. A 25% water change isnt very much, it will bring levels down by 25%. You say your nitrite is 3ppm, so even if we say there is zero ammonia it would take 3 x 50% water changes just to get the nitrite to a safe level.

2. Without knowing what your typical pH and KH was before your issue its difficult to comment. They may always have been so high or this may be due to you changing whatever you changed. If your pH and KH was lower before the change, it sounds like whatever you added in is adding carbonates/ bicarbonates into the water which raises both pH and KH. This sudden shock in different water parameters can kill fish. Once your fish acclimate to the new levels, they might be ok. Difficult to say until things settle down.

In addition your nitrate is exceedingly high. Without knowing what typical nitrate levels are from before your issue, we cant really tell if thats because of what you changed or if its always been like that. It could be down to historic over stocking, over feeding and insufficient water changes or down to what you changed. Water changes will bring the nitrate down.

What size tank do you have? What fish do you have? How many of each species? Whats a normal water change routine? How much, how often?

Products like easy balance and pH balance wont do anything to help. Its very difficult to bring pH and KH down with chemicals, much easier to bring them up. The only way to lower these to any meaningful degree is water changes with water that has lower pH and KH.

But again without knowing what typical levels are from before your issue its difficult to say what to do. If they have always been high, bringing them down will be harmful.
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