Will Gypsum cause my pound to leak? Here is why I ask and it is a long story. My pond was built about 5 years ago and is roughly .5+ acre in size with an average depth of 4ft (max depth 12ft). I used gypsum to clear the water (remove suspended clay) as it filled up and the gypsum worked. Then I stocked my pond. Somewhere in the same time frame I noticed my pond was leaking. I don't know for sure if the pond was leaking before I added the gypsum but I do know for sure that my pond had a leak afterwards. After I noticed the leak I forgot all about clearing the water and have spent the last few years trying to find/fix the leak (.5 inches per day loss and ground wet behind dam). My first attempt to fix the leak was adding 2800lbs of bentonite on the upstream side of the dam (above where the ground was constantly wet) using the sprinkle method. Needless to say, that didn't work. I then spent some more time researching ways to detect leaks. I found a few ways but unfortunately they required a 'real' liner. I had all but given up hope until this year when I ran across a company named Zonge while I was doing some more searching. As it turns out they have a way of locating leaks. I called them and spoke to them about my problem. They said they could locate the leak but most of the time you end up draining the pond to fix it. I was pretty much committed to not draining my pond so I went back to my pond builder who I had been in contact with since it was built. I explained to him of all the cost involved and we decided to give the bentonite another try. So, I put 4000 pounds of bentonite in the suspected leak area. It didn't work. Just as I was about to call Zonge and make arrangements, my pond builder came to me with an offer I couldn't refuse. He agreed to come out and reline the pond at no cost. He said he has built hundreds of ponds and has never had one leak and this wasn't going to be the first. Needless to say I took him up on his offer. A few weeks ago, he constructed a holding pond above mine and we pumped it full of water. Then we drained some more of the main pond down to where he could section it off and build another holding pond. Then we filled the second holding pond with water and moved the fish. The rest of the water was then pumped over the main dam into a ditch. A few days later after the rest of the main pond dried out, I noticed a small stream of water running down the inside of the dam. Everything around it was bone dry. This had to be the leak and it was where I had put the bentonite. My only guess is that the bentonite didn't settle there because the bank was so step. Most if not all of the bentonite looked like it settled in the deepest part of the pond. A couple of more days passed and the old pond was finally relined with clay and lots of it. He said there is no way this dude is going to leak now. So, we broke the dams of the 2 new ponds above and let the water and fish run back in. It was just enough water to cover the deepest part of the pond which is exactly where the pond had leaked down to last year so I knew the fish would survive. Then I got real lucky, the rain came and lots of it. My pond has now filled to within a couple of inches from where it was before we started the repairs a few weeks ago. The down side is that all of the clay has muddied the water. I was about to go get some gypsum and start the whole process over again when I mentioned it to the pond builder and he thought that it may not be a good idea. So, after all this I ask the experts.....will gypsum cause my pond to leak.? I think it would bond with the clay and cause it to sink.....adding more clay to the bottom. I don't think I could handle going through all this again and my wife can not even stand to hear the word 'pond'.