The 150 is set up as a cummunity right now. I like this type for a couple of reasons. (1) Variety. (2) Less problems, by this I mean when I had a species tank I would have a spell of fish dying. I had a cichlid tank and had approx. 6 dozen Sicolofy (sp?) the solid blue type, and about every six weeks or so I would lose about 6 or 8 fish. They would spawn again. A few weeks later another die off. This went on for about 5 years. Never could find the problem. Finally about 2 years ago the whole tank died. The only fish that didn't die was the common pleco.