Don’t Sump That Seahorse! Refugiums Are Not A Happy Seahorse Home.

By: | Date: 03/21/2011 | 4 Comments |
Refugium/Sump Combo

Seahorses don’t belong here.

Seahorses don’t belong in refugiums. Yet this is one of those frequently reoccuring questions that comes up repeatedly by many people considering seahorses. I’m not sure what the appeal is – perhaps the knowledge that they need a specialized setup, but not exactly what that entails or why. Whatever the reason, this article is meant to dismiss the notion and put the idea to rest once and for all, covering the several reasons why it is a bad idea.

I’ve been keeping seahorses over a decade, and been active on many aquarium message boards. I even worked in a fish store for a spell. A seahorse refugium set up is one of those irresistible temptations that way too many aquarists have to try, no matter what advice they receive. Almost everyone one is sure they can do better than those that attempted it previously. And every one fails. Here’s why.


By in  in far the biggest reason to not keep seahorses in sumps is temperature. Most people keeping a reef tank, or even a fish only tanks are going to be at higher temperatures than you should be keeping seahorses. While most seahorses kept in captivity are tropical, they actually require much lower temperatures than what you’d find them in the wild, and much lower than reef aquariums

Why? Seahorses are very prone to bacteria infections, and high temperatures, combined with the excess waste seahorses produce is a recipe for disaster. Felicia McCaulley covers the details of the relationship between bacterial infection and temperature in her article on Seahorses and Vibrio. Tropical seahorses need to be kept under 74 degrees, and 72 is probably better. Most people are keeping their tanks 78 degrees or above, which creates a dangerous situation for seahorse. Additional equipment inside the stand often create even more heat, making it warmer in the refugium than in tank. Even if its a remote refugium, chances are the temperature will only be a degree or two different form the display tank.

So what if you can keep the temperature in your sump down to a temperature suitable for seahorse? Still don’t do it. There are still a multitude of other problems that a refugium presents.


Seahorse are unbelievably messy. They have a short digestive track, which means they need to be fed 2 or 3 times a day, and their excrement is not well digested, leaving lots of waste to break down in the aquarium. They often miss much of the food added for them to eat as well. Especially if you have a reef, you don’t want the excess waste in your tank, unless you want a hair algae forest. I’m really not kidding that they’re messy, seahorse keepers are always fighting an ongoing battle with nutrient export.

What about pods in your refugium? A refugium simply can’t keep up with the voracious appetite of seahorses. Seahorses can decimate a well populated refugium in a matter of days. Which leads to another reason seahorses and sumps don’t mix – very often they’re left with the belief that a seahorse can survive off the microfauna in a refugium or aquarium. This simple isn’t the case, but being in a refugium, it becomes easier to forget or ignore their multiple daily feedings.

Wrong Environment

Another thing that shouldn’t be forgotten with seahorses is their love for space. Many refugiums & sumps are designed to be shallow so they fit in stands under aquariums. On top of that, they often have a lowered water level to allow some space in case of an overflow. Seahorses, however, do best if kept in taller aquariums. The two are often just mutually exclusive.

As it’s a refugium, it will likely be packed with algae for nutrient export – but seahorses need space, not a tangled mass of green. And reducing the greenery will likely reduce the effectiveness of a refugium anyway. Sumps/refugiums tend to have a small overall footprint. How small depends on the set up, but aquarists unfamiliar with seahorses tend to believe that the seahorses will live in just one spot. Seahorses are actually quite active, and appreciate space to roam.

Flow rate can also be a concern. Seahorses do best with a moderate flow and places they can get away from the flow and rest. Most modern keepers advocate something like 10 to 20 times turn over in a seahorse tank, but with sheltered areas the seahorses can go to rest. Often refugiums are extremely low flow – as a well set up refugium should be, but the flow is low enough that it doesn’t do enough to wash away waste and bacteria, making an unhealthy environment for sensitive seahorses. Conversely, some refugiums set up with all the water flow going through the sump passing through the refugium, creating way too much current with no place for a seahorse to get away from the rushing water.


Seahorses are still tricky fish to keep, and while Captive Bred specimens have made keeping seahorses easier, they still require extra work and extra vigilance. When things go wrong with a seahorse, it is extremely important to catch it early on. Which is just another in the long list of reasons that refugiums are not a good place for seahorses – rarely are they set up with observation in mind. Without having an easy to see display tank, its entirely possible to miss problems until it’s just to late.


Refugiums can be dangerous as well, especially if the seahorse is an after thought. Being weak swimmers, they are likely to be swept over baffles. They can end up being pulled into an unprotected pump or access to heaters where they are likely to hitch and suffer burns.

Shared Tank Systems

So now we know that refugiums are a bad idea, what about separate display tanks that are plumbed to share the same water as a reef? It is still a bad idea.

It does mitigate some of the problems exclusive to sumps and refugiums, and you can design the tank to fit the seahorses needs. However, one of the biggest threats remains – temperature. Chances are your reef will be too warm and temperatures between the tanks may only drop a couple degrees even with careful planning. And most reefers don’t really want this anyway, as it will drastically increase the nutrients in a reef tank, leading to an endless battle with various nuisance algae.

Your Reef Tank Will Suffer

For reefers, this might be the most important part. As I’ve said a few times, seahorses are waste machines. They have incomplete stomachs so food passes through with a large part of it undigested. And they have to eat a lot. You’re going to need to feed them 2-3 times a day, and the food is very nutrient rich. Skimping on feeding isn’t an option either; seahorses may last a while but slowly waste away of not properly fed, and a lot of seahorse novices miss the signs of a starving seahorse. You’ll also need to remove much of the algae used for nutrient removal, and continue to remove it as it grows, so the seahorse has enough room to move around. Now you’ve got a significant addition of waste and less nutrient control from algae. If that weren’t enough, they’re going to deplete all the pods you have in the refugium, thus leaving none to feed the main tank.

What about that one guy . . .

So you probably know someone that has or has had seahorses in their refugium. While I’d love to say that its the exception that proves the rule, chances are it’s not even that. I don’t know of any cases of really long term success with seahorses in refugiums. Seahorses should live 5-10 years, so color me not impressed when a seahorses is still hanging on after 6 months, or even a year. And I’ve seen plenty of these so called success stories – but never has the seahorse really been in the system long term.

What Now?

You found this article after you’ve already put seahorses in your refugium. What now? The question you need to ask is if you’re ready to set up another tank. You don’t have to get it set up completely today or tomorrow, but it should be in the near future. If you can’t, then finding a fellow enthusiast that can take them and put them in a proper seahorse tank.

If you do decide you want to keep them, in the short term then do what you can to adjust the refugium to make it a safer place until you’re finished setting up a dedicated aquarium:

  • Lower the main tank’s temperature as low as you’re comfortable going to about 72 °F (22 °C) over a period of a few days, no need to shock your corals or fish.
  • Put a fan over the refugium, and if it’s in a stand, keep the door open.
  • Look for equipment that could cause harm and modify it to protect the seahorses, such as intake covers on pumps and guards on heaters. Add some dulled teeth to baffles nearest to the seahorses in an attempt to keep them from going over.
  • Adjust the flow in the refugium so it’s more suitable to seahorses, either slowing down or increasing it as needed.
  • Prune excessively dense areas of algae, and make sure there are open areas for the seahorses to move.

When planning their new tank, keep in mind that a refugium is actually very beneficial on a seahorse tank. They just don’t belong in them.

Updated 9/28/2012

4 Responses to “Don’t Sump That Seahorse! Refugiums Are Not A Happy Seahorse Home.”

  1. Christy Says:

    I think the info u have post is very good, actually i pick some tips!!

  2. Jodi walker Says:

    I have been a vet tech for many years at the animals rescue league. My first love was always the ocean and Dolphins.. Im 49 and I would love to get into a hobbie such as raising Seahorses. I have a 30 gallon tank .. Hopefully you may be able to tell me everything I need to successful raise and sell seahorses. Im not worried about the money as for as the proper exquipment I may need and the tanks I may need. I appreciate your time in this matter and will be looking forward to to all the information you can send me. take care . Thanking you in advance Jodi

  3. Sharyn Gillin Says:

    Very informative information..I would appreciate any info/ help on setting up my very first marine seahorse tank. I have just purchased a 4ft tank..with all filtration built into top. Starting of with little live rock to create balanced bio cycle…

  4. Bill Goody Says:

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