Just bought a house with a pool and there are yellowish brown "stains" on the bottom. After 2 weeks of initially starting to take care of the pool, the water is balanced. When first tested, the chlorine level was 0. Water was clear. Added shock, algae (or whatever) disappeared. Stains reappeared after 2-3 days. Have some sort of "frog" chemical system. Water is crystal clear just these spots are a problem.
Attached two photos of the spots. Any advice or help would be appreciated!