My tanks have just gone crazy! Last night I lost a guppy to what I think was mouth rot. Today I've lost 3 (make that 4) CPD from the same tank. This afternoon I did a 65-70% vac and water change and did a double dose of Seachem Safe. I tested the water a few minutes ago and got some crazy colors in my vials! So as of just a few minutes ago my parameters are 20 Gal planted: pH 7.6 Ammonia 0.25 Nitrite 5+ (off the chart purple!) Nitrate 7ish GH 4 KH 3 (I've added CaribSea Aragonite but don't know how else to raise GH/KH) This is crazy! Parameters have been perfect until now. After testing just now I dosed another double dose of Safe along with a dose of API QuickStart. Do I need to do another partial water change? Edit: I just checked my 38 gal and everything is perfect except for the same GH/KH readings. So I did about a 20-25% water change and treated with Safe and Quick Start. Waited a while and did another water check. Parameters still crazy. Ammonia slightly better and Nitrite still off the chart. Installed an Emperor 400 filter (up from a Penguin 150 that never seemed to work quite right) moving my old filter cartridge and bio wheel over also. I moved the Aragonite into a media filter cartridge and will move the Matrix from the gravel into a media cartridge tomorrow or the next day, after my filter has enough time to transfer BB from the old cartridge. I just did ANOTHER water test and results are: Ammonia 0.05ish just slightly tinged greenish yellow. Nitrite still bright purple Nitrate maybe around 3. I have no idea what is going on with this tank and how I should proceed. I don't want to lose any more fish!