The brown stain means you have Iron in your pool water. To get rid of the stains, follow these steps:
1. Get your free chlorine to 0.0ppm by not adding more chlorine, this might take a few hours or days depending on the level of FC in your water.
2. Add polyquat 60 algaecide after getting chlorine to 0.0ppm to prevent algae from growing in your pool during the process that might take few days.
3. Get your pH to 7.2 using pH minus
4. Put your filter on circulation and add 1pound ascorbic acid for every 10,000 gallons pool to get stains away within 24hours.
5. Get pH back using pH increaser, then raise TA using Alkalinity increaser since ascorbic acid will reduce both
6. Add chlorine to raise your FC to around 3 to 4ppm.
To prevent more stains in future, use metal sequestrant like SC-100 by Orenda Technologies in your water. Find ascorbic acid, Polyqyat 60, and SC-100 Orenda metal sequestrant via different Amazon links here: https://dengarden.com/swimming-pools/Why-Swimming-...