Water Changes in Tank Equipment and Water problems. Posted December 4, 2007 hello again:) i bought a test kit for ammonia and nitrtite.( titration kind) and my ammonia& nitrite tested 0 ppm. so the strips were faulty!well upon cleaning my filters out twice a month instead of once a month, they act normal, not stressed anymore. When i cleaned the filter floss, it was black, and its normal color was white.... no wonder they felt like crap!( that wasnt keeping my water clean with all that dirt in it.) I was wondering what my water changes should be like? right now im changing 1/3 of the water once a week. I have 5 orandas in a 55 gallon tank, and they all are 6 inches including the tail. I feed them twice a day. Unlike our tanks that get a 90% change every day.