This was the question posed by a manufacturer of test kits and other equipment for aquarium keepers. There appeared to be no authoritative answer. We set out to get one.

The following manufacturers kindly gave us estimates of their annual production Clearseal, Aqua-Care, John Allan Aquariums, Living Pictures, Peak Aquatics, Rolf C. Hagen, Seabray, Tahiti, Underworld and Red Sea Aquariums. These were added to figures recently appearing in the trade press for Juwel (who are not members of OATA). The final overall total was 562,500. No provision was allowed for any other manufacturer thus the figure will be higher than that quoted, but by what margin it is impossible to say.