I would like to introduce a tool that I have found extremely useful in my years of aquaculturing coral. Hydrogen peroxide has been a time saver, and a life saver (as well as harbinger of near total death and destruction). For years it has been known that barley straw bales when used in ponds, release hydrogen peroxide as byproduct of decomposition. Later companies marketed barley derived algae inhibiters. I started using hydrogen peroxide as a dip, or for direct application to troublesome algae.
At first I dipped various corals that I had a lot of clones of in 3% hydrogen peroxide solution, like you get from the pharmacy. I did time trials for times ranging from 3-12 minutes. By far some of the Cnidarians (Corals, Anemones, Jellyfish…) most resistant to the hydrogen peroxide are Zoanthus sociatus type, small polyped Zoanthids. I accidently left some in 3% solution for over 45 minutes. Not long after that they were open and flourishing. Coral on the other end of this spectrum include Hydnophora, adult Pocillopora, and some Acropora. Hydnophora seem to melt almost on contact. For some reason, small colonies settled as planulae, are rather resistant to the effects of hydrogen peroxide. Adults suffer after a minute or two. Acropora have to be approached on a species by species basis. Some can’t take 30 second baths without dying back. A few species can stay in for 6 minutes with no ill effects. I recommend playing it safe with these guys at first, until you start to get a feel for it. Also most algae problems will be around the base of the colony. Here you can just use a small pipette to squirt hydrogen peroxide onto the offending algae. Coral such as birdsnest Seriatpora barely encrust, if at all, often it is easiest to clip them off and start over on a fresh plug.
If there does happen to be a spot in the middle of the colony that is covered in algae, careful removal of the algae, and rinsing with hydrogen peroxide will allow the coral to start to re-grow over the exposed skeleton. A vibrant colony of algae will produce compounds that retard the growth of the coral in the surrounding area, preventing recolonization of the skeleton with coral tissue. By killing this algae off, including algae deeper down into the skeleton, where snails, and tweezers can reach, you allow the coral to be free to grow with out direct competition from the algae.
More recently I have been using diluted doses of hydrogen peroxide. This has been helpful for species like Montipora, Acropora, and Pocillopora that show such a high sensitivity to 3% solutions.
I have been finding that hydrogen peroxide has many more uses, rather than just the removal of algae.There are many more uses for hydrogen peroxide that I will discuss at a later date, among them flatworm and nudibranchs dips, and aiptasia removal. In the meantime happy reefing.