My situation is similar to Steve32k. I have yellow stains all over the liner. My 16x75 38,000 gallon pool is surrounded by trees, oak, pine, and probably some ash and maple. I thought it was yellow algae and I used Yellow Out and shock per the instructions but the stains are still there. I don't have a place to go to test the water and am just using test strips. I added chemicals today and will test again tomorrow. I'm wondering if I should increase the chlorine level?