I heard you should use an undergravel filter. I have a 1 gallon tank with 5 Adault and 24 baby Pygmy Seahorses and I only have an undergravel filter with an airstone going down a tube in the back of the tank. My male Seahorse just had his babies on 3/8/06 it was a really neat experience to see!! He had 27 babies and 24 babies are still alive.