I've had a pool for 30 years, inground for 20 and I've had very little trouble. I've just kept my chlorine level up and it has stayed clear. My ph level was way low, maybe around 6, so I decided to use soda ash to raise it. As soon as put it in (3 lbs) the water started turning dark. The color in the filter is a rust or burnt orange color. Tried shocking (2 bags) and no change. Got any idea what it is and how to get rid of it?