I have a 55 gal community tank over a year old. Tank parameters ammonia 0, ph 6.8 to 7, nitrite 0, nitrate 5 or less. Temp 77f. I am finding fish half eaten. I have a mix of black, ember and neon tetras, a few zebra danios,5 Cory's and a 3 inch pleco, and 5 guppies.I also have 2 german rams...