Reply To: Size tank

Pete Giwojna

Dear Desa:

Yes, a 30 gallon aquarium meets the minimum size requirements for a large pair of Mustangs (Hippocampus erectus), and tall tanks like your hexagonal aquarium are a good choice for seahorses because the increased depth and hydrostatic pressure can help keep them healthy.

In short, Desa, your 30-gallon hex tank has good dimensions and has very nice water depth to help protect the ponies against gas bubble syndrome, which is very desirable. However, because the surface area in a tall, vertically oriented tank like yours is minimal, you’ll have to be extra careful to make sure the tank has plenty of surface agitation as well as good top-to-bottom water circulation in order to be sure that the tank is well oxygenated and that you don’t have any problems with gas stratification, as explained below in more detail:

The Importance of Surface Agitation

Because the height of the aquarium is an important consideration for a seahorse tank in order to allow the seahorses to mate comfortably during the copulatory rise and to protect them against depth-related conditions such as gas bubble syndrome, many seahorse keepers opt for tall hexagonal or column tanks rather than the usual rectangular aquarium setups. That’s just fine and hex tanks and column tanks can work very well for seahorses providing they are large enough and the aquarist is careful to provide them with good surface agitation in order to assure good oxygenation.

That’s important, because the amount of dissolved oxygen in an aquarium is dependent primarily on three factors: the surface area of the tank, the water circulation in the aquarium, and the amount of surface agitation in the tank. Gas exchange takes place only at the air/water interface or surface of the aquarium, which is where clean oxygen enters the aquarium water and dissolved carbon dioxide is off-gassed, leaving the aquarium. The greater the surface area of the aquarium, the more efficient this gas exchange will be, and the higher the dissolved oxygen levels and the lower the dissolved CO2 levels will be as a result. Not only does keeping the levels of dissolved oxygen high and the levels of dissolved carbon dioxide low make it easier for the seahorses to breathe, it also helps to stabilize and maintain the pH and prevent it from falling. Likewise, good circulation throughout the aquarium will prevent dead pockets or stagnant areas, assuring that all the water in the aquarium passes over the surface for gas exchange on a regular basis. Surface agitation is important because no gas exchange can take place unless the surface tension of the water is broken. Therefore, the better the surface agitation, the more efficient gas exchange becomes and the better the aquarium will be oxygenated.

This is where vertically oriented aquarium such as hexagonal tanks and column tanks are at a disadvantage. The surface area of such tanks is restricted, much reduced from the surface area of a standard rectangular tank of equal water volume. Hex tanks and column tanks thus have less surface area for gas exchange to take place, and it is very important for such tanks to have good aeration and surface agitation to compensate for this drawback. This is especially vital for the seahorse keeper, because our seagoing stallions are very vulnerable to low levels of dissolved oxygen (and high levels of dissolved carbon dioxide) because of their primitive gills structure. So if you will be using a hexagonal aquarium or column design for your seahorse tank, it’s especially important to you to provide good water circulation and surface agitation.

Employing wave makers, devices that automatically alternate the direction of the water flow, and using small powerheads to supplement water movement are all the more important when you are using a tall column tank or hexagonal aquarium. Ordinary airstones and bubble wands can also be helpful for providing surface agitation and improving water circulation, and they will do your seahorses no harm whatsoever as long as they produce relatively coarse bubbles and are positioned where the bubbles cannot be drawn into the intake for the water pumps or filters. Just keep the airstones, air bars, or bubble wands relatively shallow in tall tanks – no more than 20-30 inches deep, and they will help to maintain high dissolved oxygen levels while helping to prevent gas supersaturation.

Without devices such as these to maintain good water circulation from the top of the tank to the bottom of the tank in a vertically oriented aquarium (e.g., hex tanks or column tanks), the dissolved gases in the aquarium can become stratified. When the aquarium water cannot mix efficiently from the bottom of the tank to the surface of the aquarium, stratification will occur, with the highest levels of dissolved oxygen and the lowest levels of dissolved carbon dioxide near the top of the tank, where gas exchange takes place, and the lowest level of dissolved oxygen and the highest level of dissolved carbon dioxide building up near the bottom of the aquarium, where the seahorses tend to hang out. That is not a healthy situation for the aquarium or for the seahorses and their primitive gills, which makes efficient circulation crucial for a tall tank with a restricted surface area.

For these reasons, it’s important for the seahorse keeper who uses a hex tank or column tank to monitor the levels of dissolved oxygen on a regular basis to make sure they remain nice and high. Don’t just sample the water at the top of the tank – be sure to test the dissolved oxygen levels in the water at the bottom of the tank where the seahorses will be spending most of their time as well! We will discuss the use of test kits to monitor dissolved oxygen in more detail in Lesson 4 of the seahorse training manual.

In your case, Desa, I would suggest making sure the 30-gallon tax tank has vigorous surface agitation and then I would position a very small powerhead at the bottom of the aquarium with the water flow directed upwards, so that the powerhead provides continuous water movement from the bottom of the tank towards the top. That will help to assure that the entire aquarium is well oxygenated, and that there are adequate levels of dissolved oxygen at the bottom of the tank as well as at the surface. Just make sure that the intake for the powerhead is well shielded or screened off so that it will be safe for the seahorses.

In general, it’s a very good idea for seahorse keepers to take special precautions when using powerheads or internal circulation pumps in a seahorse tank in order to assure that a curious seahorse does not get its tail injured or damaged by the impeller for the powerhead/pump. Basically, this just means that whenever the intake for a powerhead pump is large enough to allow an unsuspecting seahorse to get its tail inside, it’s a good idea to shield or otherwise screen off the intake, regardless of how strong the suction may be, just to be on the safe side. Often this merely involves positioning the powerhead amidst the rockwork or anchoring it in place with the suction cup where there’s no possibility for a seahorse to perch on the powerhead or wrap its tail around the inflow/intake for the unit.

When that’s not possible, you may need to take more elaborate measures in order to screen off the intake from the pump are powerhead to make it safe for the seahorses, Desa.

For example, here’s how to proceed when using the Hydor Koralia powerheads, which are relatively safe compared to other types of powerheads. For one thing, since they are not impeller-operated, the intake or suction is fairly weak compared to a normal powerhead, and there is therefore no danger that a curious seahorse will have its tail injured by an impeller. Secondly, the “egg” or basket-like structure that covers the powerhead often offers sufficient protection so that an adult seahorse really cannot injure its tail. For example, the gaps in the Koralia 1 are only 1/8 of an inch wide, which is too small for grown seahorse’s tail to fit to the gaps.

Just to be on the safe side, some seahorse keepers will encase the entire egg for a Koralia powerhead in a veil-like material, especially if they have smaller ponies, as explained below:

<Open quote>
“I have a Koralia that works great in my anemone tankI have a Koralia that works great in my anemone tank(no seahorses). Just in case I bought a piece of Tulle (bridal veil material) to cover it. I got the purple tulle that looks just like coraline algae. Just cut it into a square and put it over the Koralia and secure the ends with a zip tie. Think of it like a lollipop wrapper-if the pump is the lollipop the tulle is the wrapper and instead of twisting the paper at the bottom like a lollipop you secure with a zip-tie. I have H. fuscus and H.barbouri and they could definetly hitch on the Koralia (and I have the nano) The pump still works great and nothing can get in it.”
<Close quote>

The Tulle trick will work just as well for screening the intakes of other types of powerheads or circulation pumps as well, and the bridal veil material is not so fine that it will easily get clogged up or impede the flow through the device.

Finally, Desa, since it has been a long time since you have kept seahorses, I would recommend that you read through the Ocean Rider Seahorse Training Manual before you actually purchased your ponies.

The seahorse training program is very comprehensive, consisting of several hundred pages of text with more than 250 full-color illustrations, and it will explain everything you need to know in order to keep Ocean Rider seahorses successfully in a home aquarium, Desa. We provide a free copy of the seahorse training manual to all first-time buyers and customers to assure that home hobbyists are well prepared to give our ponies the best possible care before they make a purchase. There is no charge whatsoever for this service.

If you would like to receive a free copy of the seahorse training manual, just send me a brief note offlist via e-mail at the following address, and I will send your copy of the Manual to you as an attachment right away:

[email protected]

Best wishes with all your fishes, Desa!

Happy Trails!
Pete Giwojna, Ocean Rider Tech Support

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