I have a 20 year old concrete pool that was originally finished with marcite. After 15 years the marcite was becoming rough and thin in spots. I had the marcite removed and the pool re-coated with hydrazzo. Recently I noticed a small spot in the bottom of the shallow end (about the diameter of a golf ball) that needs re-coated. I have no desire to drain the pool. Is there an underwater patch or coating to address this small spot? Thanks, Neal