It is a 29 gallon tank. He had 2 apistos and one died other than that he has 5 tetras and a mystery snail. Two days ago he added a bristle nose pleco and an algae eater. He has some floating plants, but maybe we need more. Also we have consistently checked the water and the parameters have all been normal. We were so surprised when the apisto died. The other one didn't look too good for awhile, but is perking up. He is a young teenage kid and he bought 2 fish that cost $22 each, he wants more expensive fish. I want to ensure his tank is healthy before he adds more expensive fish because I don't want him to lose anymore. Thanks for your help!