33 hex with two 303 canister what to put in for media?

[intarsiabox]

I have a little HOB filter on my nano with a filter sponge, GAC and a phosphate remover such as Chemipur Elite in it. I have crystal clear water and no bad algae, mind you I also keep up with my water changes. You could put the same in the canister. I would only use one filter and add a powerhead if you need extra flow as it costs more to double up your media needlessly and you will also have more tubes in the tank that detract from its natural look. Keep in mind that seahorses aren't good swimmers and a low flow tank is best for them.