Why is brown water blowing back into your pool?
Because the water Filter has broken inside your pool.
You have hard water, that will distort the color of your pool real easy. Have someone come and fill your pool with anything other than the water that you have already used. I am experiancing the same problem with brown water. Come to find out that the clorine oxidizes the Iron in Well water turning it brown. There are chemicals that you can get at the pool supply store that will help. Best of luck…
The "spider gasket" inside the valve has been destroyed by the chlorine and the water is blowing through the valve instead of going through the sand. Take the cover off of the valve by removing the screws on top and examine the gasket beneath. If this is not the problem, then I would replace the sand in the sand filter. Pool Masters