Since the general consensus of the respondents to this thread seems to be that Melafix is ineffective, this may not be of value to you, but for those who use it with larger tanks, Melafix for aquariums and Melafix for ponds are often the same price for equal amounts. Melafix pond is 5% Melaleuca oil while the aquarium version is 1% Melaleuca oil-same active ingredient, different concentrations. Just use the pond version, adjust the dosage as appropriate and save 80% of the cost.