I've had many customers use Fix-A-Leak. This product is poured into the water and disperses itself in such a way that it will seal tiny leaks just by circulating in the water. I am not sure if this is what you are talking about. I see a success rate of approximately 33 - 50%. I can think of one spa customer that was losing 40-60 litres per day over the winter and tried this product in March. They haven't lost any appreciable amount since. I would certainly say that it is worth a try. We only started selling it this year, and maybe sold 10 bottles with 4 or 5 being successful.

Brad
Waterworks Pools