Professional aquarists that keep seahorses and seadragons in public aquaria and zoos typically recommend a turnover rate of about 5 gallons per minute or 300 gph for their syngnathids, with the stipulation that the current should be steady (nonvarying) and one-directional so the seahorses can find sheltered, slack water zones to hold in when desired.
As long as the flow rate on the Emperor 400 Bio-Wheel is adjustable, so you could turn it down at feeding time if necessary and adjust the current to the right level for your particular seahorses, it would certainly do the job very nicely.
The nonadjustable Emperor 280 Bio-Wheel would also work well on a 45-gallon aquarium. It shouldn’t produce too much water flow or turbulence, and if desired, you can always add a very small powerhead or two to eliminate any dead spots or to direct a stronger currents toward any suitable live corals you may be keeping your seahorse tank.
In short, either the Emperor 400 or the Emperor 280 should suit your purposes if you use them properly. When it comes to water movement, seahorses don’t like overly strong currents that they have to fight while swimming or that whisk food past them too fast to scrutinize, target, and eat, but good circulation is as important in a seahorse setup as any other aquarium. You must avoid dead spots, where there is no water movement at all, without producing currents that are too overpowering.
Here’s a brief discussion on water flow in the seahorse tank from my new book (Complete Guide to the Greater Seahorses) that should help clarify this issue:
Time and time again I find that home hobby tanks have far too little water movement. In my experience, most seahorse setups are chronically undercirculated, a serious mistake for small, closed-systems aquaria, and our pampered pets often suffer as a result. Many hobbyists are overly conscious of the seahorse’s inactive life style and limited swimming ability, and have adjusted their flow rates accordingly, resulting in less water movement than desirable. In actuality, seahorses prefer moderate water movement, including some areas of brisk current, providing there are also sheltered spots and some areas of relatively slack water they can move to when desired. Slack water means comparatively low flow, NOT stagnant conditions! Avoid dead spots and stagnant areas at all costs.
I have often discussed this matter with professional divers and collectors who regularly encounter seahorses in the ocean, and they report that the horses are often found where you would least expect them — well offshore and thriving in areas with powerful currents. For example, here is how Paul Baldassano, a commercial diver in New York who makes his living collecting sea urchins, describes the behavior of his local seahorses:
"In regard to seahorses in the wild, I occasionally see Hippocampus erectus in the wild while SCUBA diving but never in the places where they are supposed to be. I see them in the open sea far from shore and also in areas with large rocks and very strong currents. The last one I saw was in a channel off the south shore of Long Island New York in water about 12 feet deep. The current was so strong that I had to hold on to the rocks so as not to be swept away. This Hippocampus erectus was having no trouble staying there munching on the abundant plankton. Apparently they find places near the rocks where there is no current because as you know they are lousy swimmers. There is also a large population of seahorses in a similar area in another part of the New York shore, but I think it is best not to divulge that location for obvious reasons (Baldassano, pers. com.)."
Neil Garrick-Maidment, a very successful seahorse breeder in the UK, reports much the same thing:
"Whenever I have dived on Seahorse sites I have always been amazed by the currents and tides that this very fragile looking Seahorse lives in. In setting up a tank for them I try to remember the feeling I had in those areas and replicate them. I have now started to use wave surge devices, so that the current in the tank, although strong (they seem to thrive in strong currents) varies in its direction (Garrick-Maidment, Jun. 2002)."
Likewise, David Warland, a fish farmer and commercial seahorse breeder in Port Lincoln, Australia, reports he often finds Hippocampus abdominalis perching on the tuna net enclosures at the farm in deep water:
"The Horses that are around the farms have traveled vast distances over plain sand/mud to get to the farms, which are in at least 20 meters of water, and are miles from the nearest land or shallow water (Warland, pers. com.)."
And Jorge Gomezjurado, the Senior Aquarist at the National Aquarium in Baltimore, recommends the following when it comes to water movement:
"I personally believe that current and water dynamics are very important for Syngnathids. In nature they live in areas with active water movement.(i.e., tides in mangrove lagoons and estuaries, coral reefs, kelp forests, etc.). Why don’t give them the same environmental conditions in captivity? Our small tanks (90 gallons) also have large turnovers on an average of 5 gpm (or 300 gph). It is very important that the current is steady and directional constant, which allows the animals to find a good spot to hold and they will not be pulling in different directions all the time."
The point is that, as long as slack-water retreats are available, the greater seahorses can tolerate far more current than most folks suspect and good circulation is as important for a seahorse setup as any other aquarium. I cannot emphasize that enough.
For example, in addition to an external power filter, my SHOWLR system also has a 200 gph powerhead with a sponge pre-filter positioned right near the top for surface agitation and extra water movement, with additional small powerheads used as needed to eliminate any dead spots along the substrate or behind the rockwork. I like to give my seahorses as much current as they can handle without getting blown around.
For your seahorse tank, I suggest the filtration should turn over the volume of the aquarium a MINIMUM of 4-5 times per hour. As long as your seahorses aren’t getting buffeted around by the currents, aren’t spilling eggs during the copulatory rise, and aren’t having difficulty targeting their prey and eating, there’s no such thing as too much water movement. Just make sure your seahorses are not getting trapped against overflows and be sure to shield or screen off the intakes for any powerheads or overflows. Powerheads can be turned off or switched off at feeding time, if necessary. [Close quote]
Best wishes with all of your fishes, Jen!