With all this talk of garlic and dying fish I thought I would also throw this into the mix
http://forum.marinedepot.com/Topic19619-10-1.aspx
I tried beta glucan with good results on my achilles tang after I had to treat him with copper for marine velvet.
The only beta glucan I could find around here was the stuff derived from oats, stuff made from brewers yeast is better i believe