Please help! Water was clear but yellow strip bottom side of pool under the skimmer and return flow. The only other issue was what looked like lines of brown dirt from center in a couple of places. This brown stuff scattered like dust when brushed. Thought it was mustard algae. FC was 4, CC zero, ph 7.8, CYA 40, alk 90. Added 'yellow clear' and one gal of 6% bleach. Next day, yellow gone, water still crystal clear but now FC is 2 and CC is 10. We have NEVER had CC higher than FC. From the info I've read, if CC is high, then there's still something in my pool, is that right? Do I need to add bleach to shock level (according to pool calculator, I'd need to add 392 oz of bleach). But water 'looks' great. What am I missing?