I started the whole, 'must go bigger' syndrome in freshwater. At one time I had about 7 freshwater planted tanks running, ranging from a 6 gallon to 2 75's. So lucky for me it wasn't an expensive set of stairsteps with the saltwater fascination. I knew I wanted a system at least the size of my largest planted tank (which was a 75) so I started from there. It's my husbands fault that I ended up with three 75's plumbed into the system.