I have a very old in-ground cement hot tub (approx. 500 gallons). I lose about a half inch of water or between 6 and 8 gallons a day. I've had the pipes pressure tested and everything was perfect. A leak detection company finally identified a web of tiny cracks in one area of the seating surface as the source of the leak. They suggested having the cracked cement ground out then refilled and resurfaced. I called the pool company that's maintained my pool and spa for 30 years. Unfortunately, spring is here and they're tied up opening and repairing pools and can't fit me in until July. I'm thinking of taking temporary action and using Flex-seal, a rubber spray well-known by anyone who watches late night TV (boat with screen door bottom). Anyway, my only concern is that the chlorine I use in the spa might attack the spray and create an additional problem (like gunk in the pipes or filter or some sort of sticky mess on the seating surface). Does anyone have any experience using Flex-seal or does anyone know of a product that might be used in its stead? Or maybe it's best to keep filling the spa and just be patient. Any advice?