Can CH rise drastically in a month?

[abehep]

Hello all.

I am first time pool owner starting last March and have been following TFP forum for almost two years. For the most part, I feel like I've had a great summer experience because of all the advice given on this forum.
So thanks again Since my pool opening, my CH started at around 450 and gradually raised up to about 575 by the first week September.
Then from September to October 20th it rose to about 750. I just tested it twice on October 24 and it is now 925.

my fill water test stats as of October 24 are: CH of 400-500, TA 180, PH 7.5

my pool water test stats as of October 24 are: FC 8.5 CC 0 PH 7.6 TA 90 CH 925 CYA 50 Temp 65

The pool is always covered. I know I need to bring my CYA up but it hasent been much of a problem with the pool always being covered.

Any thoughts to why the CH is going crazy now?

 

[bdavis466]

Your fill water is very high in calcium so every time you top off the pool you are adding more calcium. These late summer/early fall months are notorious for being both windy and very dry which drastically speeds evaporation.

There isn't much you can do unless you add a water softener to your fill water. Be sure to keep an eye on your CSI to limit the chances of scale.

 

[abehep]

It seems crazy to have the CH jump from 725 to 925 in a week with no swimming and minor evaporation as it is always covered. Does this sound possible?

2nd questions,
It seems i've read on here that the CH can still be quite high and still maintain a good CSI. At what point do I need to look at water replacement?

 

[mknauss]

It seems crazy to have the CH jump from 725 to 925 in a week with no swimming and minor evaporation as it is always covered. Does this sound possible?

2nd questions,
It seems i've read on here that the CH can still be quite high and still maintain a good CSI. At what point do I need to look at water replacement?

I assume you did not use any CalHypo in the pool ----

I find that once my CH reaches 1000 ppm it is more difficult to manage CSI. My fill water is CH 250 and TA 130. And I add water pretty much all the time.

I know that when I get to the high reading of CH the testing gets a bit more variable. Drop size from the reagent bottle has an effect. So testing error may be able to account for some of the drastic rise.

Take care.

 

[pooldv]

The only other option can think of is if there was some scale build up in the pool and you kept your pH lower during that period the scale might have dissolved back into solution.

More here about scale, Pool School - Calcium Scaling

 

[JoyfulNoise]

Have you been using any metal sequestrants or scale inhibitors in your pool?

 

[abehep]

I did not use any cal hypo. I’ve only used my swg and muriatic acid all summer. I have an automatic fill so I’m not sure how water has been added. It shouldn’t be much as the pool is always covered with water temps in the high 60’s.
Its interesting you mentioned drop sizes. I tested my fill twice and got 400 the 1st time and 500 the second.

 

[mknauss]

You have evaporation in your area no matter what your water temperature due to low humidity. Same as in my area. The cover helps, but with fill water that high in CH, you start with high CH and with any evaporation it only goes higher.

Take care.

 

[AftonJeeper]

Maybe you have a leak? Try shutting the auto fill off.

 

[abehep]

Maybe you have a leak? Try shutting the auto fill off.

I haven't noticed anything but that is certainly a possibility. I will shut off the autofill to see if and how much water is needed to replace.

- - - Updated - - -

Have you been using any metal sequestrants or scale inhibitors in your pool?

no I have only added muriatic acid and CYA this summer along with my swg

 

[mknauss]

A leak would actually reduce your CH rise. As you would be replacing your pool water with fill water. With evaporation the solids in your pool water (salt, calcium, CYA) stay behind and you then use fill water which increases your CH. If you had a leak you would have been adding salt and CYA all summer.

Take care.

 

[JoyfulNoise]

no I have only added muriatic acid and CYA this summer along with my swg

One last question - are you performing the CH test correctly? The correct way to perform the test is to add drops of R-0012 titrant until the blue color stops changing hues of blue. Many people do the test by stopping as soon as they see the color change from purple to blue; that is incorrect. Like the TA test, you keep adding drops until it stops changing color. This type of testing error usually only causes a 2-3 drop difference, so it would not entirely explain the jump in CH. Since the jump in CH is significant, then I would say it's real unless your reagents are very old and there is some kind of testing error from that.