Why does CH drop?

[nolefan]

I have been maintaining my own pool using the information on this site since the beginning of June. It has never looked better and I am getting the hang of it. My CH has been holding steady at 300 since i started. But over the last 3 weeks, it has slowly started dropping off. It measured today at 250. Where does it go? Does the pool use it? It has been raining a lot over the last few weeks and I have been dumping the excess water. Did I just answer my own question? Do I need to add more CH to bring it back up as I dump water?

Thanks for the Help:

FC: 5.5
TC: 0.5
PH: 7.6
CH: 250
TA: 70
CYA: 70

 

[Bama Rambler]

It has been raining a lot over the last few weeks and I have been dumping the excess water. Did I just answer my own question?

Yes, you did. If you've been having to drain water you're also draining CH.

I would watch it and if it gets much lower than 250 I'd bump it back up to ~300.

 

[anonapersona]

You are also draining CYA and TA. Should have seen them each decrease by some 1/6th as well.

(edit for clarity) Since you are having so much rainwater added to the pool, that rain, with 0 CYA and 0 TA ought to be diluting the pool and as you drain off the excess, some of that CYA and TA is leaving, just like the CH has. So, I would be expecting those levels to have changed a bit also, at least to the extent of the accuracy of the CH testing that shows you lost 50 ppm of 300 ppm. That is, if you are using the sample size that has one drop = 25 ppm CH, then your accuracy is less than if the sample used means one drop = 10 ppm CH.

None of this is critical, just a comment to watch those other numbers as well.

In winter it is usually wet here and I see all these values go down together.

 

[nolefan]

You are correct. All those levels have dropped as well. Somehow I didn't correlate it to me dumping the water.