Tuzz,
Have you tried Cutrine plus? There are probably other equally good products but Cutrine has worked very well for me in the past. No way I would ever use copper sulfate in my ponds, but Cutrine doesn't pose as much danger from the copper as straight copper sulfate...from the label:
"The ethanolamines in CUTRINE-PLUS prevent the precipitation of copper with carbonates and bicarbonates in the water. Waters treated with CUTRINE-PLUS may be used for swimming, fishing, drinking, livestock watering or irrigating turf, ornamental plants or crops immediately after treatment."
