I have 7 fish in a 6x2x2 foot species tank. Approx 600 Imperial Litres (dont know what that is in US Gallons). Lots of PVC and ceramic pipes and caves. They squabble but not too much and the smallest is about 35cm. Bare bottom tank for easier maintenance but I keep some ice cream containers full of 8mm gravel to collect eggs. They arent very demanding fish but great to watch.