Chemical reaction confusing

[CarlD]

You are assuming that you aren't fighting something else. Your chlorine dropped a lot, fast. That tells me your best move is to shock the pool again.

[donaldm823]

You are assuming that you aren't fighting something else. Your chlorine dropped a lot, fast. That tells me your best move is to shock the pool again.

I reshocked again at 1615 yesterday with a 180oz jug of chlorox (2.8ppm). Based on chemistry this morning my chlorine was constant over night (FC=4.78 and TC = 4.92). It appears no chlorine demand overnight as my add should have taken the pool to approx 4.9 and the CC also went down, so the drastic decrease from yesterday is still unexplained.