We just switched our 29G FW planted tank to a 40. We were using a Fluval 204 on the 29 but gave that to my sister who bought a 25G cube tank. We are now running a Fluval 304(rated up to 75G) on the 40G. Fish seem to be doing well and water is clear. But is the 304 a little too much for the fish? It definitely puts out some water flow.