A sudden drop in FC: Cause and effect

[dschlic1]

Thursday evening I tested my pool for chlorine and pH. Normally I see a variation of a few tenths of a ppm change from day to day. However on Thursday I had a drop of almost 1 ppm! This worried me and go me to thinking about why the drop. I then realized that the day before I filled to pool. I fill with tap water, and in my area, tap water usually runs around 3 to 4 ppm of CC.

So it looks like the CC in the fill water dropped my FC by 1 ppm. I am going to have to remember in the future to add 1 ppm FC when filling the pool.

 

[anonapersona]

I've read that more and more public water systems are switchingover to Chloramine to treat tap water. Chloramine is chlorine combined with ammonia.

 

[chem geek]

Yes, the 3-4 ppm CC would consume around 1.5 to 2.0 ppm FC (perhaps a little more) as chlorine oxidizes the monochloramine in the tap water.