We have a 55 gallon freshwater tank. Currently stocked with 4 tiger barbs, 4 neon tetras and 2 red swordtails. Our tank has been running for approximately two months. We are also using a stone aerator in the tank and the filter has a biological wheel filter attached. In the beginning we had two cat fish, 5 tiger barbs and 2 angel fish. Our newbie error was stocking the tank with too many fish too soon. The only fish that survived were 4 of the tigers. We believe it was the high ammonia levels that did the damage. We have done many water changes and have added Ammo lok to decrease the ammonia. Seems like no matter how many water changes we do (we do condition the water before it is added), we cannot get the ammonia level to 0. We feed them flake food twice per day. Morning and night. They eat everything we feed them in less than two minutes. I would think that the biological filter would have come around by now, but the ammonia level continues to read 4.0. The tank is crystal clear. All of the fish appear to be healthy with the exception of the tiger barbs color fading, but it comes back in a day or two. What could we be doing wrong? Any suggestions?