How to Set Up a Seahorse Tank

Updated February 21, 2017

Seahorses have fascinated people for centuries. Seahorse heads resemble those of horses on land, and they move unlike most other sea creatures. To set up an aquarium that will maintain seahorses, you will need to pay attention to several critical factors. Seahorses require a certain water temperature and tank size. These creatures also are prone to stress if not given the proper holdfasts and hideaways. In addition, the calm nature of seahorses can conflict with other fish and even rough waters.

Purchase a tall tank that is at least two and a half to three times the length of the uncurled body of the seahorse. Seahorses will often rise upwards as they copulate. Several pygmy-sized seahorses can be kept in a 5- to 10-gallon tank; place up to six medium-sized seahorses in a 24-gallon tank.

Place substrate along the bottom of the tank. Substrate are the rocks or sand that line the bottom of the tank. Allow a path along the bottom of the tank for the seahorses to travel.

Put a biofilter in the tank. A biofilter could be a live rock or canister filter. These objects will help filter the water. Make sure the biofilter doesn't have any sharp edges that could injure the seahorse.

Position holdfasts and hideaways throughout the tank. Seahorses become stressed if they can't hold onto a living or plastic plant with their tails. Holdfasts should be tall and have many limbs, or branches. Hideaways should be large enough for a seahorse to enter into and hide, but not occupy a tremendous amount of space in the tank.

Create salt water for the seahorse. Purchase sea salt that is designed to be mixed with R/O water. (R/O stands for reverse osmosis and this type of water is available at aquarium supply stores). Measure 1/2 cup of salt per gallon of water. Insert tip of a hydrometer into the water to measure the salinity; the salinity must be between 1.024 and 1.025.

Measure the water temperature with a thermometer. Tropical seahorse species require a stable temperature between 23.8 to 25.5 degrees C. Subtropical species require the water be kept between 21.1 to 23.3 degrees C. Temperate species require a lower water temperature between 18.8 to 22.2 degrees C.

Measure the pH range with a pH meter. Insert the tip of the pH meter in the aquarium, the pH must measure be between 8.0 to 8.3 to be safe for seahorses.

Insert a powerhead in the aquarium to create a low-strength current. Seahorses are not agile swimmers and don't take well to strong currents. If the seahorses are thrashing about the tank, the current is too strong; turn down the powerhead.

Place a lamp near the tank. Seahorses should have 10 hours of daylight, which can be produced by allowing light to filter in from nearby windows. They also need three hours of half-light and eight hours of darkness. Place a lamp a few feet away from the tank to produce half-light.


Replenish evaporated water from the tank with clean, fresh water, not salt water. All supplies needed for the aquarium set-up are available at pet or aquarium stores.


Don't keep fast moving, agile, active feeders or aggressive fish with your seahorses. Seahorse are kept best with fish such as dragonnetes and blennies. Never place seahorse with puffers, butterfly fish, damselfish or angelfish.

Things You'll Need

  • Tall aquarium
  • Substrate
  • Biofilter
  • Holdfasts
  • Hideaways or tank structures
  • R/O water
  • Sea salt
  • Measuring cup
  • Hydrometer
  • PH meter
  • Powerhead
  • Lamp
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About the Author

Si Kingston has been an online content contributor since 2004, with work appearing on websites such as MadeMan. She is a professional screenwriter and young-adult novelist and was awarded the Marion-Hood Boesworth Award for Young Fiction in 2008. Kingston holds a Bachelor of Arts in English from Mills College.