A few days ago, I started noticing yellow spots/stains on the wall of our deep end. I tried brushing over the weekend, but this didn't seem to have any effect (no dust clouds or anything). The water is checked & chlorinated every day with bleach, and remains crystal clear. The only chemicals that we've added to the pool since buying our house in June are 8.25% bleach and 20 baume muriatic acid periodically to lower the pH (creeps up frequently).
Below are my numbers from today's tests (TF100):
FC - 7 (just added bleach to bring up to 9, where I prefer it to be)
CC - 0.5 (bringing FC up to 9 usually 0's this out)
TA - 100
CH - 860 (haven't checked this in weeks. It's high because previous owner used cal hypo weekly)
CYA - 50
pH - 7.4
Any thoughts on what these yellow spots could be?