Re:Switching Tanks

Pete Giwojna

Dear Haynes:

I think it is a terrific idea to relocate your seahorses from the 12.5-inch tall 30-gallon aquarium into the taller 20-inch high 30-gallon instead. Sooner or later they would’ve had chronic problems with gas bubble syndrome (GBS) in such a shallow aquarium. A 20 inch tall setup is much more suitable for seahorses, but as long as you are contemplating moving your seahorses into a taller 30-gallon aquarium, why not consider making it a 30-gallon Extra-High All-Glass Aquarium (24"L x 12"W x 24"H) instead? With a height of 24 inches, the Extra-High All-Glass Aquarium would be even better.

Relocating the seahorses shouldn’t be a big deal if you will be transferring the biofiltration, intact and fully operational, from the one 30-gallon aquarium to the other. For example, if live rock was providing the biofiltration in the 12.5-inch tank and you are transferring all the live rock to the taller tank along with the seahorses, that should work fine. Or if you were using a bio-wheel or a filter with bio-balls or a canister filter to provide the biofiltration in the 12.5-inch tank, and you will be transferring that filter to the new aquarium complete with all the biological filtration media and a full complement of beneficial nitrifying bacteria intact, then the transfer should go well.

In those cases, the stocking density and total volume of the two aquariums would be the same, and carefully transferring the biofilter with the seahorses should assure that there are no ammonia or nitrite spikes and that the nitrogen cycle is not disrupted during the move. No problem.

However, if you are planning on leaving the 12.5-inch aquarium up and running with its biofiltration left in place, and then transferring your pair of seahorses to a new, taller 30-gallon aquarium which has not yet been cycled, that’s a recipe for disaster. The new tank will certainly experience ammonia spikes, eventually followed by equally high nitrite spikes, and the use of a nitrogen cycle accelerator isn’t going to prevent that.

The reports I have received from hobbyists who have tried adding cultures of nitrifying bacteria or other products that are supposed to boost the population of beneficial bacteria and accelerate the cycling process have generally been very disappointing. Judging from the feedback I received from hobbyists, those products simply don’t seem to work as advertised. The word I get is that new tanks seems to take nearly as long to cycle fully when those products are used as they do when they are not.

I think it’s a wonderful idea to transfer your pair of seahorses into the taller aquarium, Haynes, and I strongly encourage you to make the move. But you’ll need to either cycle the new aquarium before you transfer the seahorses, or transplant the biofiltration from one tank to the other, with the biofilter intact and fully operational, in order for the move to go smoothly with no problems.

A 20-inch tall is a huge upgrade over the 12.5 inch tall tank, and your seahorses will be much healthier once they have settled into the taller aquarium. The suggested stocking density for Mustangs and sunbursts (Hippocampus erectus) of average size is one pair per 10 gallons of water, so you’re new 30 gallon aquarium would be large enough for you to gradually increase your herd, Haynes. Once you’ve gained more experience with seahorses, the 20-inch tall 30-gallon aquarium can safely support up to three pairs or six individual seahorses. But I would suggest going slowly and adding no more than one additional pair of seahorses to the new aquarium once it’s up and running smoothly until you’ve been working with seahorses for a while longer. It’s always best for new seahorse keepers to keep their tanks somewhat understocked in order to maintain a bigger margin of error while they are learning than it is to stock their setups to capacity.

In general, sea urchins are quite inoffensive and do a good job of controlling algae in the aquarium. But like all echinoderms, they require pristine water quality and must be acclimated to the aquarium very carefully over a period of several hours, preferably via drip acclimation. They will not do well in an aquarium without abundant algae or in one that has high nitrate levels.

I have never had occasion to keep urchins with seahorses, so I can’t speak from personal experience when it comes to their compatibility. But when it comes to seahorses, I think the pincushion urchins should make great tankmates, providing you can meet their dietary requirements, which means a tank with lots of algae for them to dine upon. Personally, I think the long-spine urchins (Diadema species) would also do well with seahorses, although some folks caution against them to the possibility that the seahorses may accidentally impale themselves on their sharp spines. I suspect that risk is overstated, however, and is more of an imagined danger than an actual threat. For example, seahorses in the wild are known to associate with urchins and seem to regard them as part of the substrate, commonly even using them as hitching posts.

In fact, Tom Bowling has observed all ages of H. tristis on sea urchins, from newly settled juveniles to fully-grown adults, an unusual form of commensalism never before reported for seahorses (Bowling, pers. comm.). He believes they remain with the urchins throughout their lifetime (Tom Bowling, pers. comm.). Bowling reports the seahorses actually perch amidst the spines and ride around on the sea urchins, feeding on schools of larval shrimp and other small crustaceans. In their deep-water environment, the urchins apparently provide them with shelter and a microhabitat that attracts small crustaceans and tiny fish, creating a wide range of feeding options for the seahorses (Tom Bowling, pers. comm.).

I think I would be inclined to avoid the pencil sea urchins and club or urchins when it comes to seahorses, however. They are much more carnivorous than the other urchins, which tend to be strict herbivores. Pencil urchins will feed on sessile animal life, particularly once they’ve depleted all will be available algae, and I once saw a pencil urgent capture and consume a small horseshoe crab in an aquarium. It’s conceivable that they could also pin down the tail of a seahorse and do serious damage with their bony mouthparts.

So in general, I think pincushion urchins such as the Blue Tuxedo Urchin (Mespilia globulus) would do fine with seahorses providing you can provide them with adequate water quality and a sufficient supply of algae. The only danger I can possibly see from them would be accidentally toppling over a piece of coral or live rock and accidentally pinning a seahorse beneath it. And if you get small pincushions the chances of that seem very slim. And I think long-spined sea urchins would probably be all right as well, except for the same risk of toppling things over, but some hobbyists may prefer to be perfectly safe and avoid them to eliminate all danger, however slight, of a puncture wound from their spines. And I would tend to stay away from pencil urchins and club urchins due to their carnivorous tendencies.

Best wishes with all your fishes, Haynes! Upgrading to a taller seahorse tank is the best thing you can do providing it is fully cycled before you make the move.

Pete Giwojna

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