Yes, I think adding a small powerhead or two to eliminate dead spots and stagnant areas in your seahorse setup is an excellent idea, and it can help to reduce your problem with nuisance algae. For example, here’s an excerpt from my new book on seahorses that discusses water movement and circulation in the aquarium:
Powerheads & Water Circulation
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.
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.)."
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 entire volume of the aquarium a MINIMUM of 3-5 times per hour, preferably more. 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 screen off the intakes for any powerheads. Powerheads can be turned off or switched off at feeding time, if necessary. [End quote.]
The red algae you have noticed in your aquarium is actually a type of cyanobacteria, which is often associated with excess nutrients in the water. Using a feeding station or target feeding your seahorses, and diligently cleaning up any leftovers afterwards can avoid this. An efficient team of aquarium janitors and scavengers can also be a big help with the tidying up. Let me know if you would like some more detailed feeding suggestions that can help you reduce the nutrient load in your seahorse tank.
Best of luck with your seahorses, Kathyrn!