I have had my 55 gal for about 2 years now. I had issues at first setting it up but haven't had anything wrong in over a year. no fish losses. I changed my filter and did a water change and left my fish in the care of my sister for 2 weeks while on a wedding/honeymoon cruise. when I came back all my fish were acting funny and I changed my filter again b/c it appeared to be dirtier than normal. I will admit that I cleaned off the part of the filter that I'm not supposed to and I changed the carbon. I tested the water and got a high ammonia reading. I'm guessing it was around 4ppm. the highest on my tester. so it could have been higher than that. I had a small amount of nitrite. the second or third color on the chart. the water was light purple in the tester. I don't have my tester here to look at the numbers. the nitrate was around 40ppm I think. but I have always had a problem with nitrate. it never seems to go down and the tester always stays dark red. I'm using the apI master tester the one with the test tubes and droppers. I vacuumed the rocks in hopes to get rid of ammonia. still high. then I found a pretty large fish dead a few days later. about 8 inches a black shark and then I started losing more fish. since I had came home I was doing water changes almost everyday of about 25% with no improvement of the ammonia. I got the nitrite out after a few days but now almost 2 months later the ammonia is still at about 2 or 3 and when I stop changing the water it gets higher. help I don't know what to do. I am planning on moving my fish to a 220 gal but I don't want to stress them out. I haven't lost a fish in about a month but I'm sure they are probably not happy with those water conditions. oh and I have also used amquel and I had to put copper in the water to treat a small outbreak of ich and I have used stress coat and aquarium salt. even though the ammonia may be locked how do I get rid of it and why is it this high. do I need to cycle my tank even though its established. help!!