Hi I just introduced fish into my aquarium and they are not doing well. I don't know what is wrong and they are dying! They don't seem to look unhealthy other than they may be a bit listless. I bought 9 black tetra, 3 otto cats and 4 ghost shrimp. 5 of the tetra died and now one of my otto cats doesn't seem to be eating. I have a low-tech tank, 26 gallons with crypts, anubias and one amazon sword. They seem to be doing well. my ammonia is close to zero, pH is 7.2. I do not have a test kit for Nitrate/nitrite, but the LFS tested it for me on Saturday and said it was zero. Is the PH a problem? any suggestions? I did a 20% water change yesterday when I saw that I lost some of the black tetra. Could definitely use help!!!