Liquid chlorine raises pH ?

[eransh10]

Hi all,
My PH is usually around 7.8-8.0 and around 7.6 if I add 8oz of acid per week.
My Alk is flat 80 doesn't move a bit (which is fine by me).
I am using the BBB methode and until now (I got the house with the pool at Nov) I only had to add acid and chlorine.
Today I had an issue with my pump and the pool guy who fixed it, told me that using liquid chlorine will cause the pH to raise, and this is probably the main reason why my pH is so high.

Is this true ?

Should I try and use chlorine tablets instead ?

Thanks for you input about this.
Eran.

 

[JasonLion]

Stick with bleach.

Technically, bleach does raise the PH right when you add it, but then as the chlorine gets used up the PH comes back down. Over time the PH change from bleach is very nearly zero. Trichlor tablets will leave the PH more or less alone when first added and then the PH will come down as the chlorine gets used up, so the net effect is that the PH goes down. That might be a good thing in your situation except that trichlor tablets also add CYA, which will get too high and cause problems eventually.

PH tends to rise for two reasons. New plaster, less than one year old, will constantly raise the PH as it cures. This happens very quickly for the first few weeks and then much more slowly for the rest of the year. Also, any kind of aeration, from a SWG, spa jets, waterfall, fountain, rain, etc, will cause CO2 to outgas, which raises the PH. The rate at which CO2 outgases depends on the TA (higher TA -> faster PH rise), PH (lower PH -> faster PH rise), and amount of aeration (more aeration -> faster PH rise).

 

[eransh10]

Stick with bleach.

Technically, bleach does raise the PH right when you add it, but then as the chlorine gets used up the PH comes back down. Over time the PH change from bleach is very nearly zero. Trichlor tablets will leave the PH more or less alone when first added and then the PH will come down as the chlorine gets used up, so the net effect is that the PH goes down. That might be a good thing in your situation except that trichlor tablets also add CYA, which will get too high and cause problems eventually.

PH tends to rise for two reasons. New plaster, less than one year old, will constantly raise the PH as it cures. This happens very quickly for the first few weeks and then much more slowly for the rest of the year. Also, any kind of aeration, from a SWG, spa jets, waterfall, fountain, rain, etc, will cause CO2 to outgas, which raises the PH. The rate at which CO2 outgases depends on the TA (higher TA -> faster PH rise), PH (lower PH -> faster PH rise), and amount of aeration (more aeration -> faster PH rise).

Thanks for your tip.
My pool was built in 1993 so there is no new plaster issue here.
I just wonder why my pH goes up all the time. Is it OK for it to stay at around 8.0 with alk of 80 ? Or should I add acid on a weekly basis ?

Oh - and I forgot to mention that I have a waterfall but it is turned off in the last few months.

 

[duraleigh]

My pH rises constantly as well. Last fall, I decided to let it seek it's own level and it went above 8.2+ Ouch!

I have no idea why. Now SWG and no aeration....it just rises.....albeit very slowly.

You mentioned using Tabs (pucks). Whats' your CYA ppm? If it's low you could maybe use them a little but you'll need to monitor CYA.

 

[Ohm_Boy]

I seem to recall that Ben had some info about maintaining high ph in pools. I'll see if I can find a link, but I think he was actually recommending ph over 8 if you were using chlorine and no copper. Anyone remember the details?

[edit] Found it. http://www.poolsolutions.com/gd/hiphpool.html [/edit]

 

[JasonLion]

As PH goes up it becomes more and more irritating to your eyes, chlorine becomes less effective, and there are increased risks of staining and scaling. There can be significant advantages to running with PH above 7.5, but I don't recommend going above 7.8 or maybe 7.9.

When Ben did that write up the relationship between PH, TA, and CO2 outgassing was not understood. With that new understanding it seems to be more effective to lower the TA more than Ben's system would, which allows the PH to stay lower than the system Ben was proposing.

 

[Guest]

I seem to recall that Ben had some info about maintaining high ph in pools. I'll see if I can find a link, but I think he was actually recommending ph over 8 if you were using chlorine and no copper. Anyone remember the details?

[edit] Found it. http://www.poolsolutions.com/gd/hiphpool.html [/edit]

The High pH pool info that Ben had was based on the Hamilton Index from United Chemical. Interestingly enough, Ben also pointed out that most of United's bromine based products need a high pH to operate properly. Just remember that high pH is the MAIN indicator of scaling conditions. If you look at the Hamilton Index a few things become evident. First, they use Total Hardness which is going to be HIGHER than calcium hardness and if you look at the TA readings they are on the low side and the higher the hardness the lower the TA is run, actually much lower than normally recommended. so in effect they are saying run a lower CH and a lower TA and a higher pH. This is not really out of line with the LSI or CSI.