A standard aquarium filter for biological, mechanical and chemical filtration can be used for seahorse tanks. All types of standard aquarium filters will work (internal filters, external filters, canisters and/or protein skimmers, etc). Follow manufacturer recommendations for the filter size/model that fits your aquarium style and total water volume.
It is important to monitor your filter intake to make sure it isn’t overpowering your seahorse’s ability to swim (if intake is overpowering your seahorse, rubber-band a filter pad over the entire intake to reduce flow). If you purchase an aquarium kit, a filter is typically provided. Make sure to regularly replace the filter pad/media as a part of your maintenance routine.
There are several filter model features that we recommend for seahorses: