So I've had a bustling healthy planted tank set up for almost a year now, and just in the past month I've been experiencing serious die offs which include two 4-year-old angelfish and four 2-year-old Bloodfin tetras. My first angel died about a month ago, then my bloodfins all went in the same night about a week ago, and I've just found my last angel dead a few hours ago.
20 gallon tall tank
I have an API master test kit which ensures me that my water parameters are spectacular.
I do a 25% water change once a week with tap water treated with API water conditioner.
I fertilize my plants via PPS pro method with macros (Magnesium sulfate, Mono Potassium Phosphate, Potassium Nitrate & Potassium Sulfate) & micros (Plantex CSM+B).
DIY C02 with 2 2L yeast mixture bottles. I diffuse the C02 into my tank via Aquaclear 30 HOB filter.
Temperature is kept steady at 78 degrees F
flora - Heavily planted with anubias, bacopa, cabomba, amazon sword, wysteria, and some plant I cant identify.
fauna (still surviving) - a few nerite snails and two Oto cats
Is it possible that I've been killing my fish via C02 poisoning? I just switched from a Hagan C02 diffusion ladder to the HOB diffusion so maybe the increase in dissolved C02 is killing my fish? I have a HOB filter so I think that my water should be sufficiently oxygenated...
Strangest part is that I have an Oto cat that has so far survived everything, and I thought that they were supposed to be the most sensitive!
Does anyone have any ideas? At this point I think that maybe I have some sort of disease floating around in my aquarium (although all of the dead fish appear perfectly healthy, except for the being dead part...). I think that I'm going to treat with antibiotic from the LFS before I put any more fish in and see if that helps...