Re:Setting up my very first 10G. seahorses tank

Pete Giwojna

Dear Alex:

Pixies or dwarf seahorses (Hippocampus zosterae) are the first seahorses I ever kept and are still among my very favorites. No bigger than your thumbnail when fully grown, I find their diminutive dimensions to be charming in the extreme! Whenever I set up a dwarf exhibit, I find it endlessly fascinating to witness the seahorse’s entire cycle of life taking place in microcosm, and I spend countless hours marveling at the spectacle of miniature seahorses courting, mating, giving birth, newborns, the juveniles and young adults all thriving and growing right alongside the old warhorses.

Yes, sir, if you provide them with good water quality and plenty of newly-hatched brine shrimp to eat, you can keep your dwarf seahorses (Hippocampus zosterae) well past the year mark. As a rule, dwarf seahorses are relatively short-lived compared to the larger breeds of seahorses. In their natural habitat, the life expectancy of these miniature marvels is only about a year, but this is one seahorse that often enjoys a greater life span in captivity than in the wild.

In nature, winter storms and hurricanes take a heavy toll on their numbers, and very few adult dwarf seahorses survive their first winter; none are known to overwinter twice (Giwojna, Jun. 2002). A detailed field study marked all the individuals of a Cedar Key population and followed them closely for a period of several years (Strawn 1958). The study revealed that the Cedar Key dwarves grew fast, reached sexual maturity early (within 3 months), and died young, with few surviving for more than a year (Strawn 1953; 1958). No 2 year-old specimens were ever observed. (Strawn 1953; 1958)

Thus, their natural life span is believed to be about one year in the ocean. In captivity, experienced hobbyists often keep them for 2-3 years. With good care, some dwarves make it well past three years of age, and not only can they survive to that ripe old age, they are still going strong and may even keep breeding well into their third year. So you may certainly aspire to keep your dwarf seahorses longer than one year, Alex.

I’ll try my best to answer the rest of your questions one by one below:

(1) Yes, sir, you certainly can use two of the sponge filters, one at either end of the tank, to provide the chemical and biological filtration for your dwarf seahorse setup. The sponge filters are air-operated and shouldn’t generate too much turbulence or current for your dwarf seahorses at all. I find that sponge filters are the most efficient way to filtered for seahorse tanks of 5 gallons or less, but there are a few precautions you should bear in mind when selecting the sponge or foam filters for your 12-gallon aquarium.

Be sure to avoid sponge filters with weighted bottoms or other metal components since they will rust when exposed to saltwater. Sooner or later this will cause problems in a marine aquarium (sooner in the small setups that are most suitable for H. zosterae). Select a sponge filter that has no metal parts and is safe for use in saltwater. The proper units will have suction cups to anchor them in place rather than a weighted bottom.

The sponge filters I find that work well are the Oxygen Plus Bio-Filters (models 2, 3, 4, or 5) or the Tetra Brilliant foam filters. They have no metal components, making them completely safe for use in saltwater, and just one of these foam filters will do the job on a tank of 5 gallons or less. They do not have a weighted bottom but are equipped with suction cups instead. Two of the smaller models can be used on larger tanks like yours, Alex, but one of the larger models, like the one at the link below, would be sufficient for your 12-gallon aquarium:

Click here: Foam Aquarium Filters: Oxygen Plus Bio-Filter 2

Avoid the Oxygen Plus Bio-filter 6, 11, and the Multi sponge, which all have a weighted bottom (metal), that rusts when exposed to saltwater. If you want more filtration, you’re better off going with two of the smaller suction cup sponge filters rather than any of the models with weighted bottoms. For instance, for a 12 -gallon tank, I’d suggest using two well-established foam filters, one at either end of the tank for the biofiltration, just as you are planning, Alex.

All you need to operate sponge or foam filters is an inexpensive, diaphragm-operated air pump (whatever is available at a reasonable price from your LFS will do just fine), a length of airline tubing to connect the air pump to the foam filter(s), and a set of air valves (gang valves) to regulate the air flow to the filters. That’s all — nothing to it! The inexpensive Apollo 5 air pumps work great for sponge filters, but whatever air pump you have on hand should certainly do the job.

Cleaning the foam filters is a snap. Simply immerse them in a bucket of saltwater and gently squeeze out the sponge until it’s clean and releases no more sediment or debris. (I use the saltwater I siphoned out of my aquarium when performing a water change for this, and clean my sponge filters whenever I change water.) Run a bottlebrush through the inside of the tube, wipe off the outside of the tube, and you’re done. The filter is ready to go back in the aquarium with no impairment at all of the biofiltration. Takes only a couple minutes.

I like to keep a few extra sponge filters running in my sump or a refugium at all times. That way, I’ve got instant, fully established, portable biofilters I can use wherever needed — a hospital ward or quarantine tank, a nursery tank or rearing tank, a brand new setup, or anytime the biofiltration needs a boost in another tank for any reason. Very versatile! You’ll never realize how valuable an instant biofilter can be until you really need one.

However, Alex, a 12-gallon tank is a very spacious aquarium for dwarf seahorses, and there are other filtration options you can consider for an aquarium that size that may be even more efficient than the sponge filters you are considering. Contact me off list and I will be happy to run through several other simple filtration systems that work well for dwarf seahorses and may be more suitable for a relatively large dwarf seahorse tank like yours. Let’s make sure you get your dwarf seahorse tank up and running with a simple, inexpensive filtration system that will provide you with the best possible margin for error!

A water temperature of 75°F would be great for your dwarf seahorse tank, but you’ll want to raise your pH a bit to around the 8.0-8.2 range. You’ll also need saltwater test kits to measure the levels of ammonia, nitrate, nitrate, and pH, as well as a hydrometer to measure the specific gravity or salinity of your dwarf seahorse aquarium. (Your freshwater test kits won’t work on a marine aquarium, Alex.)

(2) No, sir — as Leslie pointed out, sponge filters that have been cycled in freshwater will not work in a marine aquarium. The beneficial the nitrifying bacteria that carry out the nitrogen cycle and provide the biofiltration in your sponge filters are entirely different species in freshwater and saltwater. The freshwater bacteria that are populating your sponge filters now will not survive in saltwater. You will need to cycle your dwarf seahorse tank from scratch, which is a process that can take anywhere from 3-6 weeks depending on how you proceed. Here is some additional information to help guide you through the cycling process, Alex:

Cycling the Aquarium

Until it has cycled, your aquarium will be unable to support life. Cycling simply means to build up a healthy population of beneficial bacteria in your tank that can carry out the nitrogen cycle and breakdown your fishes’ waste products.

Ammonia (NH3), nitrite (NO2), and nitrate (NO3) are all nitrogenous (nitrogen containing) wastes. All living aquarium animals whether they be fish or invertebrates excrete these wastes, and they are also produced by the decay of protein-containing organic matter (uneaten food, detritus, dead fish or inverts, etc.). The nitrogen cycle breaks down these wastes in a series of steps into nitrogen gas (N2) which leaves the aquarium as bubbles.

The nitrogen cycle begins with ammonia, which is highly poisonous. In the first step of the cycle, Nitrosomonas bacteria reduce ammonia to nitrite, which is also very toxic. In the second step of the nitrogen cycle, Nitrobacter bacteria convert the nitrite to nitrate, which is relatively harmless but becomes harmful when it accumulates in high enough levels. In the third and final step of the cycle, denitrifying bacteria then convert the nitrate into completely harmless N2, which of course bubbles out of the tank as nitrogen gas. In this way, thanks to the nitrogen cycle, dangerous wastes are converted into progressively less harmful compounds and finally removed from the aquarium altogether.

When we set up a new aquarium, and wait for it to cycle, we are simply allowing a big enough population of these different types of bacteria to build up in the biofilter to break down all of the wastes that will be produced when the aquarium is stocked. If we don’t wait long enough for the cycle to complete itself and the biofiltration to become fully established, and hastily add too many specimens to a new aquarium too soon, they will die from ammonia poisoning or nitrite toxicity. This is such a common mistake among us impatient aquarists, that when fish get sick and/or die from ammonia/ntrite poisoning, it is commonly called the "new tank syndrome."

When your aquarium has completely cycled, the ammonia levels will stay at zero because, now that your biofilter is fully established, there is a large enough population of aerobic (oxygen loving) nitrifying Nitrosomonas bacteria to reduce all of the ammonia to nitrite as fast as the ammonia is being produced. The nitrite levels will likewise stay at zero because there is also a large enough population of aerobic (oxygen loving) nitrifying Nitrobacter bacteria to convert all of the nitrite to nitrate as fast as the nitrite is being produced.

The nitrate levels ordinarily continue to build up, however, because there are simply not enough anaerobic (oxygen hating) denitrifying bacteria to convert all of the nitrate that’s being produced into nitrogen gas (N2). Since nitrates are being produced faster than they can be transformed to nitrogen gas, the excess nitrates accumulate steadily in your aquarium. That’s perfectly normal, since the denitrifying bacteria that carry out that final step, the conversion of nitrate (NO3) to nitrogen (N2), are anaerobes that can only exist in the absence of oxygen. For our aquariums to support life, and for the fish and invertebrates to breathe and survive, our tanks must be well aerated and well circulated so that there’s plenty of dissolved oxygen in the water at all times. That means there are normally very few areas in our aquariums where anaerobic denitrifying bacteria can survive, limiting their population accordingly (which is generally good, since some anaerobes produce deadly hydrogen sulfide gas during the decay of organic matter and would poison our tanks if allowed to proliferate).

Consequently, most aquariums lack a sufficient population of anaerobic denitrifying bacteria to complete the nitrogen cycle and convert nitrate to nitrogen as fast as the nitrates are being produced. The only way to keep the nitrates from building up to harmful levels in such setups is with regular water changes and by harvesting Caulerpa or other macroalgae periodically after it has utilized nitrates for growth. Overcrowding, overfeeding, or under filtration exacerbate the problem by resulting in more nitrates being produced and more frequent water changes being required to control the nitrate levels.

Live rock helps because the oxygen-poor interior of the rock allows anaerobic denitrifying bacteria to grow and break down nitrates. A deep live sand bed (DLSB) also helps because anaerobic denitrifying bacteria can flourish and break down nitrates at a certain depth below the sand where oxygenated water no longer penetrates, but a DLSB can sometimes be difficult to set up and manage properly if you’re inexperienced with live sand. Both live rock and deep live sand beds give aquaria denitrification ability — the ability to complete the cycle and convert nitrate to harmless nitrogen. Ordinarily, about 1-2 pounds of live rock per gallon is recommended – that amount of LR will provide your aquarium with all of the biofiltration you need, as well as significant denitrification ability. You will keep nitrates at harmless levels by performing regular water changes, harvesting Caulerpa macroalgae periodically, and good aquarium management.

Prepare your aquarium for cycling by setting your system up with just freshwater at first, attaching the equipment and apparatus (filter, aeration, circulation, heater, skimmer, lighting, accessories) and testing it all for a day or so to make sure you have everything in place, and that it works. Once assured that everything’s operating properly and there are no leaks, go ahead and add the substrate, salt mix, and aquarium décor, and leave everything running for a good week, allowing the various components and water to "settle in" before adding your microbes and "seeding" the tank with beneficial bacteria that will eventually establish your biofilter.

If you are using live rock, it contains all the bacteria needed to seed the tank, so all you have to do is position the live rock in attractive arrangements, provide a source of ammonia to feed the beneficial bacteria, and wait for the population of nitrifying and denitrifying bacteria to build up and stabilize.

If you are not using live rock, there are a number of different ways to seed the tank with bacteria and feed it with ammonia so cycling can proceed. Two popular methods are the fishless cycle, which I recommend, and the use of hardy, inexpensive (i.e., expendable) fish to produce ammonia and cycle the aquarium. Often used for this method are marine damselfish or mollies, which can easily be converted to saltwater. Both are very hardy and generally survive the cycling process, but I find this method to be needlessly hard on the fish and exposing them to the toxic ammonia and nitrite produced during cycling certainly causes them stress. Damselfish are far too aggressive and territorial to leave in the aquarium afterwards as tankmates for seahorses. Mollies are a possibility, but they really look out of place in a saltwater setup.

So all things considered, I suggest you try cycling your tank without fish. It’s really very easy. To use the fishless cycle, you need to add something else that will increase the ammonia level so the nitrifying bacteria can build up. I like to use a piece of cocktail shrimp (regular uncooked eating shrimp from the grocery store) and leave this in the tank to decay during the whole cycle. The decaying shrimp produces plenty of ammonia to kick-start the cycling process. This method should work great for cycling your dwarfs seahorse tank, Alex.

After about 3 days after you add the shrimp, you will notice a spike in ammonia levels until the Nitrosomonas bacteria build up enough to break down the ammonia. When that happens, you will notice the ammonia levels rapidly dropping. (If for some reason your ammonia does not hit the top of the charts initially, you may want to add another piece of shrimp.)

The byproduct of ammonia is nitrite, and during this stage of the cycling process, as the ammonia falls, you will have a corresponding increase in nitrites until the population of Nitrobacter bacteria builds up. Nitrite levels will then fall as the Nitrobacter convert the nitrite to nitrate.

It is important to use your test kits every day or two when cycling your tank to monitor the progress of the process. As described above, at first you will see a rapid rise in ammonia levels with no detectable nitrite or nitrate. Then, as Nitrosomonas bacteria begin converting ammonia to nitrite, the ammonia levels will fall and nitrite readings will steadily rise. Nitrite levels will peak as the ammonia drops to zero. Next, Nitrobacter will begin converting the nitrite to nitrate, and your nitrite readings will fall as the level of nitrate rises. Finally, after the nitrites also read zero, you are ready to stock your tank. At this point, your ammonia and nitrite levels should both be zero, nitrates will be building up, and algae will usually begin to grow. This will tell you that your biofilter is active and functioning properly, and that you can now safely begin stocking the tank. It generally takes about 3-6 weeks to cycle a tank this way from scratch.

If you any more questions about cycling, the following link should provide you with answers:
Click here:

(3) The dwarf seahorse setup you’ve outlined sounds good, in general, and could certainly be successful, but for best results, I would suggest making a couple of changes.

For example, I agree with Leslie that your dwarf seahorse tank will be better off without the live rock unless you treat it with fenbendazole (Panacur) before you put it in your tank. Dangerous hitchhikers such as Aiptasia rock anemones, mantis shrimp or predatory crabs, bristleworms, and especially hydroids, are very likely to enter your aquarium along with the live rock. All of them present a risk to dwarf seahorses and should be avoided at all costs.

If you are planning on using live rock in your dwarf seahorse setup, then it is a very good idea to prep it first using a hypersaline dip followed by a bath in fenbendazole. The hypersaline dip will drive out most mobile pests such as mantis shrimp or crabs, while the fenbendazole will eradicate stinging animals such as hydroids, Aiptasia rock anemones, and bristleworms, all of which can be harmful to dwarf seahorses. The fenbendazole will soak into the poorest live rock, and provide long-lasting protection against hydroids and Aiptasia as a gradually leaches out of the rock again. Let me know if you need any instructions on the proper procedure for "debugging" your live rock with fenbendazole before you introduce into your dwarf tank.

Secondly, I recommend that you include plenty of macroalgae and marine plants in your dwarf seahorse setup, either in place of the live rock or in conjunction with live rock that’s been pretreated with fenbendazole to make it safe for your seahorses. In the wild, H. zosterae is restricted to seagrass microhabitats in shallow water, and is typically found living in association with the seagrass Zostera, for which the species is named.

Dwarf seahorses therefore feel right at home in a well-planted aquarium that simulates their natural seagrass habitat well. For example, a lush bed of assorted Caulerpa dominates the rear third of my current dwarf tank, completely concealing the filters. The Caulerpa consists of various long-bladed and plumed or feathery varieties such as Caulerpa sertularioides, Caulerpa mexicana, Caulerpa ashmedii, Caulerpa serrulata and Caulerpa prolifera. The center of the tank is aquascaped with more macros — mostly red and gold species of Gracilaria (Hawaiian Ogo), plus a seahorse tree centerpiece and yet more Caulerpa. Other decorative macros are arranged in the foreground of the aquarium where the light is brightest: a cluster of Merman’s Shaving Brushes (Penicillus capitatus) and a stand of Halimeda sea cactus, interspersed with Udotea palmate fans. The result is a colorful macroalgae garden with a very nice contrast of colors (reds, yellows, greens, and brown) and interesting shapes. A tank heavily planted with macros such as these is a lovely sight and mimics the dwarf seahorse’s natural seagrass habitat very well.

As an added benefit, the macroalgae act as an excellent form of natural filtration, supplementing the sponge filters, and reducing the available levels of phosphates and nitrites/nitrates. When we prune and trim back the fast-growing Caulerpa regularly and remove the clippings, we’re actually exporting phosphates, nitrates and other nutrients from the tank, thereby helping to maintain good water quality.

Finally, I would suggest that you consider increasing the number of dwarf seahorses you will be starting out with. Unlike the larger breeds of seahorses, dwarves are colonial seahorses that are accustomed to being surrounded by others of their kind.

The suggested stocking density for dwarf seahorses (Hippocampus zosterae) is two pairs per 1 gallon (4 L) of water, so theoretically a well-filtered 10-gallon aquarium is spacious enough to house up to 20 pairs or 40 individual adults. In a pinch, a 10-gallon tank can support many more dwarves than that. For instance, pet dealers must occasionally crowd large numbers of fish together in cramped quarters due to a lack of space, including dwarf seahorses. Robert Straughan was once forced to keep 300 H. zosterae in a 10-gallon tank in such a situation back in the old days, and was pleasantly surprised to find that over 100 of them managed to pair off and breed nonetheless. He reported that at any given moment, dozens of dwarves were actively engaged in courtship, so it was a common sight to witness several couples rising simultaneously to exchange eggs, and that one or more of the gravid males would be delivering young virtually around the clock (Straughan, pers. comm.)!

For all practical purposes, however, it is always better to understock your aquarium than the push the envelope and test the limits of its carrying capacity. In actual practice, I find 25-30 adults can be maintained in a typical 10-gallon set up before water quality becomes problematic (especially if your are raising the young with their parents). Rather than sponge filters, I prefer to use an undergravel filter in conjunction with a very small power filter for a heavily stocked 10-gallon dwarf tank such as that. For such a system, I use an undergravel filter with a single uplift tube and mate the intake tube from the power filter to the UG uplift, so that all the water that goes through the filter first passes through a gravel bed 2-3 inches deep. That simple modification both improves the efficiency of the undergravel filter and prevents the power filter from engulfing dwarf seahorses or their food supply. The small power filter allows filter media such as polyfilter pads and a good grade of activated carbon to be used in the dwarf tank.

In your case, Alek, you will find that your 12-gallon aquarium appears quite barren with only 4 dwarf seahorses in it, and I would suggest that you start out with at least three or four pairs instead of only two. Dwarves breed best in large groups and are the most sociable of all the seahorses. What makes it extra fun is that these pint-size ponies are as prolific as they are promiscuous. Any time you have an adequate number of H. zosterae together — say several pairs — and conditions are to their liking, mating is a foregone conclusion.

With the small tanks that are best for dwarf seahorses, I find that it is very beneficial to practice an accelerated maintenance schedule. For example, I do small weekly water changes on my dwarf tanks of 10%-15%, rather than the monthly or bimonthly water changes I perform on large setups, but the volume of the water exchanged is so small — just a gallon or two at most — that they are a breeze. Other dwarf seahorse keepers go one better and make tiny water changes amounting to just a couple of pints on a daily basis. The weekly water changes you are planning should work well for a 12-gallon dwarf set up, Alex.

They have been a couple of other discussions on the Ocean Rider Club message board regarding dwarf seahorses that you might also find to be of interest, so please check out the following links when you have a chance:

Click here: – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:Dwarfs – Ocean Rider Cl,com_simpleboard/Itemid,/func,view/catid,2/id,1000/#1000

Click here: – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:pixies – Ocean Rider Cl,com_simpleboard/Itemid,/func,view/catid,2/id,1216/#1216

I have a lot of other information on dwarf seahorses and the best setups for larger dwarf tanks like yours that I would be happy to share with you if you contact me personally, Alex. They are a large files that are a bit too big for this discussion forum, but if you send me a quick note at the following email address, I will be happy to forward them to you to make sure you get started off on the right foot:

[email protected]

Do you have a copy of Alisa Abbott’s guidebook (Complete Guide to Dwarf Seahorses in the Aquarium, 2003, 144 pages) yet, Alex? That’s one book every Pixie owner and dwarf seahorse keeper should have on hand. I proofed Alisa’s dwarf seahorse book for TFH publications and wrote the preface for it, so I’m quite familiar with her guide, and I highly recommend it.

Best of luck with your dwarf seahorses, Alex!

Happy Trails!
Pete Giwojna

America's Only Seahorse Aqua-Farm and One of Hawaii's Most Popular Attractions

Ocean Rider seahorse farm is a consistent Trip Advisor Certificate of Excellence Award Winner and "Top 10 Things To Do" Kona, Hawaii attraction. Our "Magical Seahorse Tours" are educational and fun for the whole family.

Tour tickets are available for Purchase On-Line. Space is limited and subject to availability.

small seahorse 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.

Seahorse Hawaii Foundation

Inspiring ocean awareness by saving the endangered seahorse and sea dragons around the world from extinction through conservation, research, propagation, and education.

Help us save the seahorse and the coral reefs they live in with a tax deductible contribution to the Seahorse Hawaii Foundation. You will be helping to protect and propagate over 25 species of endangered seahorses, sea dragons and friends.

Make A Tax-Deductible Donation Today!

A Different Kind of Farm (Video) »

Ocean Rider Kona Hawaii

Ocean Rider Kona Hawaii
Seahorse Aqua-Farm & Tours

73-4388 Ilikai Place

Kailua Kona, Hawaii 96740

Map & Directions


Contact Ocean Rider

Copyright ©1999-2023
All Rights Reserved | Ocean Rider Inc.

My Online Order Details

Purchase Policy

Site Terms and Conditions