The water comes in through a 2" pipe at the top, drops down one level to a small pond-like area (about 2'x3') before going over into the pool. This is about 30 years old and probably has been patched a few times with mortar or possibly hydraulic cement. I noticed (after cleaning it out) that the bottom of the small pond it was sealed with something, black and looks like it may be rubberized. Hard to say. I was about to use hydraulic cement, but after getting a closer look and reading the label, it really isn't suitable as I don't think just going into the joints between the boulders would be sufficient. It also can't be used as a skim coat (which is what I want to do) and you have to chase the cracks to a minimum of 3/4". That would literally mean cutting through boulders. Not going to happen, so that's out. I'm quite sure that I need to cover up the joints with a sealer like what is in the bottom. I've thought about using roofing cement (which would definitely be waterproof) but it warns that bits of asphalt will erode away in water and become water soluble. I'm really not looking forward to more junk getting into the pool-- I have enough as it is. I've seen products like Pond Armor, which is an epoxy sealer, that look like they would probably work. I've also seen various types of pool paint. I know I can walk into a local pool store and pick up a gallon of paint (although maybe not in black). Just not sure what would work best here, so I'm looking to see if anyone has had similar issues and has found a practical solution. I really need to get this fixed, as I'm having to top off the pool probably 2 inches a week (approximately 14x30 pool). Sorry about the poor quality picture. I can get better pics if anybody needs them, but at the moment it's all I've got.
Also, as long as I'm asking, does anyone know of a good sealer that might freshen up the look of the boulders? They're in several areas around the pool, and just look kind of dull.