PH Issue

Hello! I have 4 fish tanks - one 55 gallon, two 10 gallon and one 5 gallon. Across the board I am having an issue with KH and PH. The 5 gallon is the only one holding steady right now but it’s empty because the PH crashes killed all the shrimp and I moved the betta. The other three have different stocking and planting. The two ten gallon have lighter planting and light stocking. The 55 gallon is pretty heavily planted and stocked. Probably too heavily stocked right now. I will do a water change and the KH and PH will be 2-3 and 7-7.5, but by day 2 after the water change, the KH is zero and PH is 6 but possibly lower because my liquid test kit bottoms out at 6. I have crushed coral in all three tanks. I’ve used buffers. I have done hours of reading and gone to a speciality fish store for help, but they were stumped also. I have no idea what is causing this and I have no idea how to fix it. I’m so frustrated.

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That sounds so frustrating, sorry. When KH hits zero in 2 days in every tank, I’d suspect your tap water is very soft and has almost no buffer, so the tanks use up whatever little KH they get.


I’d test your tap KH and GH first, and your nitrates too. Nitrates build up fast in a heavily stocked tank, and the process behind them eats KH. Crushed coral is also slow and often not enough by itself.


What I’d try is buffering the new water before it goes in the tank, so you start at a steady KH every time. Smaller, more frequent water changes would help too.


What are your tap KH/GH and nitrate readings? That would tell us a lot.

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