I purchased one of them. Just tested it and it is quite accurate. You might want to open up the coroplast and take a look just in case it is a cracked tank. It doesn't happen, but a quick look to make sure won't hurt. Use a drill with a socket to remove the screws and washers. A good very bright flashlight. Make sure your overflow lines are pushed through the coroplast bottom as well. If they are not, that would be your water source in the belly.