We bought a house with an inground pool just under a year ago and it's my first pool ever. On the inside just a few inches from the water level in the concrete we have a small (maybe 1/2 in) hole and water drips from it all the time. I call it the side of the pool deck. The dripping water turns green and thick (like honey thick) green gunk oozes out. I've cleaned it but it comes back. So should this hole be there, can I plug/fill it with something and what would that something be? Does anyone think this stuff is toxic?