Mustard colored algae + Free Chlorine question

Benkg43

Well-known member
Mar 2, 2021
76
Richmond,TX
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
Last night I realize I had neglected brushing my pool for over two weeks. The result was mustard-colored algae in over 50% of the pool. I immediately poured in ~.5 gallons of liquid chlorine and then brushed the entire pool. Then I put the vacuum in there for a four-hour session. Then I shocked the pool before bedtime and started another 4-hour vacuum session. By that time the pool was looking pretty much back to normal.

This morning the pool still looked good. I brushed more and started another 4-hour vacuum session. Just now I tested the chemicals. FC was between 1 & 2. PH was ~8.0. CC is 0. The FC measurement surprised me considering how much chlorine I added last night. I went ahead and loaded up 8 chlorine tablets. I avoid using those but in this case I need FC, so why not. I also threw in some MA to fix the PH.

Question... why was my FC so low this morning? My mind tells me its because the FC "ate up" the algae, thereby lowering that number. Is that right? Or???
 
FC loss is due to organics or UV.

Remember that using trichlor increases the SLAM level FC.
 
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