Hi, Illyoung! Glad to hear your ich problem cleared up. As to the tank size, your O's will likely grow quite quickly. You have a couple of things to watch. The first is nitrates. Oscars eat a lot, and waste a lot. As they grow larger, they naturally produce a lot of waste, which then pollutes the available water, largely via the nitrogen cylcle -- ammonia/nitrite/nitrate. Your tank will eventually develop bacteria to deal with the ammonia and nitrite, but the only bacteria that will break down nitrate are anaerobic, and so far we haven't come up with a safe way of keeping these in a freshwater aquarium. Though not as toxic to fish as ammonia or nitrite, you need to keep the nitrate levels to 20ppm or less -- otherwise your fish start having health and other problems. Two big Oscars in a 55 make it quite difficult to keep nitrates within a healthy range without frequent, large (over 50%) water changes. Most of us just don't have the time or fanatacism to keep up with the number of water changes to keep up with that kind of biomass in that small amount of water, ergo the recommendation for larger tanks. The greater water volume buys you time between changes. Add a dempsey and a pleco -- also large waste producers -- and the problem increases.
The other situation to keep an eye on is aggression. Cichlids are territorial, and larger fish generally need larger territories. With your mix, as they grow could very well see some violence that you probably wouldn't in a larger tank.



