I have a 20′ x 8-1/2′ x 4-1/2′ deep fiberglass (white) indoor swim spa. 30″ sand filter, UV light, electric heater. Pool temp is kept around 89-92.
I work with dogs (35 week) who have mobility issues.

I am having trouble keeping the pool clean. It has a yellow stain on the entire pool. I do a complete water change every 6 months. This time after 4 months the pool looks very bad. When I drain the pool I clean it with Acid Magic or Boat Magic, which works very well.

Since the pool is inside there are no issues with algae. Also the heater is electric so there are no copper piping.

My question is — Is there a product I can add to the water that will clean the pool short of draining and cleaning? Pool Magic?