Dear Agate:
A protein skimmer is a very useful piece of equipment for the seahorse keeper to have, but it is by no means a prerequisite for keeping seahorses successfully.
Assuming you are interested in the greater seahorses such as Mustangs on Sunbursts (H. erectus), rather than any of the miniature breeds such as Pixies or dwarf seahorses (H. zosterae), the recommended stocking density is usually1 pair of Mustangs or Sunbursts per 10 gallons (~40 liters) of water. This means that a 55-gallon aquarium is spacious enough to comfortably house about five pairs of adult H. erectus or up to 11 individuals.
However, in your case, I would want to reduce that figure a bit due to the lack of a protein skimmer, and then further reduce it to reflect the fact that you are new to seahorse-keeping. Taking that into consideration, I think you could easily keep about three pairs of adults or six individual Mustangs or Sunbursts in your 55-gallon acrylic aquarium and still maintain a reasonable margin of safety.
It sounds like you will be running a fairly basic filtration system in your 55 and relying primarily on water changes to control nitrates. There will be no Deep Live Sand Bed (DLSB) to provide denitrification, no algal filter or denitrator in a sump, and no protein skimmer to remove organics before they enter the nitrogen cycle. This limits the carrying capacity of the tank and makes an accelerated maintenance schedule and more frequent water changes an absolute necessity. I would suggest performing small weekly water changes of 10%-15% rather than larger monthly or bimonthly water changes.
A lush bed of macroalgae will also help control nitrate and nuisance algae. Macroalgae use nitrate for growth just like plant fertilizer and pruning the macros regularly is a good way to export nitrate from your system.
Don’t broadcast feed, scattering Mysis throughout the tank. Instead, target feed your seahorses or use a feeding station. Don’t overfeed, cleanup leftovers promptly, and observe fast days religiously. An efficient cleanup crew will also help.
If you’re willing to limit yourself to about half a dozen seahorses, at least initially, and observe some of the basic precautions outlined above to help compensate for the lack of a protein skimmer, your 55-gallon aquarium should make a very successful seahorse setup.
Best of luck with your new seahorse tank, agate!
Happy Trails!
Pete Giwojna
Ocean Rider, Inc. is an Organic Hawaiian-Based Seahorse Aqua-Farm & Aquarium that Follows Strict Good Farming Practices in Raising Seahorses and Other Aquatic Life.
