So the past weekend I noticed my FC level dropped to zero. I assumed I might have something blooming. Although the water is crystal clear and blue. So I added some liquid chlorine and did an overnight test. It went from about 5.5 to zero overnight. Still completely clear. But I shocked the pool, brought FC up about 20 ppm. Within 8 hours (daytime) it dropped to 8 ppm or so. Brought it back up and it dropped again. I've been battling this for 4 days.
Although it appears the drop is less pronounced now. Today I started at 20 ppm at about 8am, at 7pm it tested at 14.5 with the salt system on. So it's still losing. Again, the water is crystal clear. There is no sign of green or clouding what so ever. Filter also not dirty.
I do have a salt system. And my CYA was low...40ppm, which might have explained why it disappeared initially.
CC was at 2 ppm at the start...it's now testing at 0.5.
PH, CH, and TA are all within normal range.
Anyone have ideas where the FC is going? Could this be an ammonia problem?