This tank has been set up for almost two year now with no problems so all the stuff I've been doing has been working. I have a 55 gal with 2 marineland penquin 350s. The filter cartridge gets replaced every 3 or 4 weeks and the whole filter gets taken apart and washed out out of algae and skum every 2 months or so. I have sand substrate. A rock wall and driftwood with two java ferns as my aqua scape. Fish wise I have a couple angels, some red and black skirt tetras, some zebra danios, 2 Cory cats, clown loach, ellipse catfish which is a big boy, a kuhli loach and a pleco. In the past week I have lost 2 Balas, 2 black neon tetras, a gorami, and a guppy. I don't think all 6 of them would have jumped out. One day they are there and the next day there not. Guess my bottom feeders are getting rid of the body's. I usually fill the tank as needed for water and then every couple weeks let it evaporate 20% and them I fill back up. Been doin this method for a while now with no problems and now this all of a sudden