Actually, I only have them in 2.5 Top Fin Retreat Tanks but I'm extremely impressed with how this piece of equipment has been working They sulked in Anything bigger, I tried. The finnage on the Male makes it difficult for him to travel far for surface oxygen I've found smaller Aquariums a lot more Beneficial for this species As for the price This pair before shipping cost me $100.00 I had to Outbid someone who was also interested in the Male and I BIN The female so I didnt have to go through another high priced Auction