marine aquariums

I already responded to this on your other thread but just found this one. 55 gallons is definitely not too small for a saltwater tank! Really you can do saltwater in any size tank but the smaller ones are tougher to care for since there's not as much water to dilute any impurities and such. Most knowledgeable people feel that 40 gallons is a good minimum for the majority of people especially if they're just starting out in the hobby. The size issue I was concerned with is how many large fish he had stocked in there before the heater malfunction. As a general guidline most experienced hobbyists suggest adding up how many inches all the fish should be full grown then allowing 3 gallons of water per inch of fish for saltwater for a fish only tank. If he wanted to do a fish and corals type of tank (a reef tank) the most commonly advised rule of thumb is 5 gallons of water per inch of fish because corals need much more pristine water conditions than the great majority of fish. I heartily recommend using liverock too if he doesn't have any! It makes for a more natural environment for the fish plus it acts as an additional filtration system due to the beneficial bacteria it contains!