Greetings, Sensei of swimology. I have a concrete pool-about 10 years old. This year (I think possibly due to the extraordinarily mild winter), our algae was a nightmare to get under control. To achieve clear water, we did a few rounds of shock at 100oz Day 1, 70 oz Day 2 , and 30 oz Day 3. Our pool is 39,000 gallons. Finally, the pool is clear and the water is well balanced. But we have a lot of algae that is adhered to the walls & floor that simply will not brush off-and is still green. We do brush it & the water clouds up until the filter pulls out the algae that is floating, but we still have algae embedded. Our filter is a DE system, about 2-3 years old. For the last couple of years, we moved away from the stabilized tablets because our water was "over-stabilized" to quote our local guy. How do we remove the embedded algae? Thank you.