Transferring your Ocean Rider seahorses to better quarters should not present any problems. Preadjust the water in the 20 gallon aquarium to the same temperature, pH, and specific gravity or salinity as their present tank, and you won’t even need to acclimate them.
Of course, being handled, uprooted abruptly, and transferred to strange new surroundings is always somewhat stressful for seahorses. But in your case, no shipping stress whatsoever will be involved, and your pair of seahorses will be transferred together, which will make much less dramatic, so things should go quite smoothly and they should adjust to their new environment quite quickly. Make sure your 20-gallon setup has plenty of hitching posts and lots of shelter and sight barriers to give the seahorses a sense of privacy, and I can foresee no difficulties with the upcoming move. In time, your seahorses should really appreciate the move into more spacious quarters that are twice as big as their old tank. That’s a nice upgrade you’re planning and I heartily approve!
My recommended stocking density for H. erectus is 1 pair per 10 gallons (~40 liters), so a total of two pairs or four individuals is about right for your new setup.
I’m sorry to hear about the hair algae that’s proliferating in your 10 gallon aquarium. It can indeed be very tenacious and difficult to eradicate once it gets out of control. Sea hares will chow down on green hair algae, so a Sea Bunny may help you eliminate the hair algae, but then you’ll have to supplement its diet once the algae is gone.
The main thing when combating hair algae is to cut down on the excess nutrients in your tank. If you have to, use Phosphate Reducer to remove excess phosphates and a Poly-Filter Pad (from Poly-Bio-Marine Inc.) to remove excess nitrates. For more details, check out the suggestions from the following thread from an earlier thread titled "Hair Algae," which you can find at the following URL:
If your tap water quality leaves something to be desired, then consider buying reverse osmosis/deinonized water (RO/DI) for topping off and water changes instead. Most well-stocked pet shops that handle marine fish sell RO/DI water as a service for their customers for between 25 and 50 cents a gallon. For example, WalMart sell RO/DI water by the gallon for around 60 cents. Even my drug store sells RO water nowadays.
Natural seawater is another good option for water changes. Like RO/DI water, natural seawater can be purchased at fish stores for around $1.00 a gallon, depending on where you live. It sounds expensive, but when you consider the alternative — paying for artificial salt mix and RO/DI water and mixing your own saltwater — then natural seawater is not a bad bargain at all. It has unsurpassed water quality and seahorses thrive in it.
Just remember that Reverse Osmosis (RO) or Deionized (DI) or RO/DI is very soft and must be buffered before it’s used so it won’t drop the pH in your aquarium when it’s added.
Here are some online articles with tips and suggestions for controlling outbreaks of such nuisance algae:
Click here: CyanoControlFAQs
Check out the articles, use phosphate reducer to eliminate excess phosphate and a Poly-Filter Pad to remove excess nitrates, and use only phosphate-free, low ash activated carbon.
If you can get a seat here, then bolster your cleanup crew with additional snails and/or micro-hermit crabs that eat slime algae and other types of nuisance algae. Astrea snails, red foot moon snails, and Scarlet reef hermit crabs (Paguristes cadenati) all fit the bill and would be good additions in that regard.
Introduced as soon as possible to a new aquarium, as soon as the ammonia and nitrite levels are safe, Astrea snails effectively limit the development of all microalgae. In other words, they are good at eating diatoms, but will consume red slime and green algae as well. The Scarlet Reef Hermit Crab (Paguristes cadenati) is a colorful micro-hermit that’s a harmless herbivore. So cannibalism isn’t a concern at all for these fellows, nor are they likely to develop a taste for escargot. As hermits go, most of the time the Scarlet Reefs are perfect little gentleman and attractive to boot. I even use them in my dwarf seahorse tanks. Best of all, they eat all kinds of algae, including nuisance algae such as red, green and brown slimes, as well as green hair algae.
Best of luck eradicating your nuisance algae program, Harry!