This is a photo of a tank getting ready for seahorses! The following is my tank set up. It is not what you would call conventional, but it works! In the seahorse tanks, for all big breeds, is 1 corner filter with air stone, and 1 sponge filter with air stone, crushed shell, and IF I feel the need to, a temporary use of a Duetto filter. Other than that, I use the plastic wood like branches that are made for birds. There is one in the photo for you to see. They are easy to clean, and have a range of hitching sizes for the horses. I also keep carlerpas (alage) in the tank, and a Mexican Turbo snail to eat all the alage. That is my basic seahorse tank set up. Simple, and easy, and cheap too! :)
The corner filter can have Chemi-Pure filter media, or now I use a filter "sandwich" of nitrate remover, scavenger, and plain old carbon. Floss of course too! The carbons "sandwich" stuff handles my chemical filtration, the sponge and shell sub-straight the biological, and the air stones are the mechanical filtration. So, all 3 types of filtration are present, working, and the seahorses are happy! With the pigmies the only filtration is a sponge filter with air stone! The seahorses swim a bunch, as the current is not too heavy for them.