I've also heard of it being used to help supress cyano growth. It's very powerful in salt water as compared to it's strength in fresh water (I'm basing this on dosage comparison only, so I could be off base). Albert Thiel once recommended using it to raise the redox potential of the tank water in the event of a power failure or if things otherwise fouled... - I've tried this, and it works to such effect, but don't do it without monitoring very carefully with an ORP meter...'course this was back when some also advocated adding 15% peroxide to the water to keep it shiny clean and the ORP high, so don't use this info as good advice, as you could shock your tank pretty badly. Also, I believe certain creatures could be quite sensitive to any sudden change in redox potential (ORP). In the case you mention, I'd guess it's efficacy would be realized by helping to maintain the water quality (possibly through the oxidation of dissolved organics and thus lowering the overall burden of the tank in terms of it's biological oxygen demand?? ...I really don't know)... Probably best to just keep an eye on the water quality and do water changes as necessary. People seem to be getting good results by using garlic remedies for ich.