There are chemicals you can use to seal leaks in pools such as, dies to help find pool leaks, and patching compounds that work well fixing cracks in pool or spa shells. The best product to use to seal cracks in pools is our Pool Patch. Pool Patch is a hydraulic cement that expands when it cures so it does an excellent job sealing leaks. Regular cement based patching compounds shrink as they cure, thus they don’t work very well for patching cracks or sealing leaks in the pool shell. We don’t recommend using epoxy to seal cracks in pools.