pH question

[CanuckPool]

We have had our IG vinyl pool for about 1.5 months now. It has an SWG.
Its approx 14,500 gallons.The first few weeks it saw moderate usage and we had to keep adjusting the pH levels down, so far normal. Now the past 1.5-2 weeks the usage has gone down to light, maybe 1 swim every 2 days average and light bather load. The SWG is normally set at 60% but I have managed to get away with 40%. In any case the chlorine levels seem to be going up. Tested it with my kit and its always off the chart now 5+, before it used to be in the 4-5ppm. The real question is that the pH seems to be stuck at 7.1 - 7.2 and hasnt moved in 2 weeks. Is it because the bather load is lighter and the weather is cooler, we do tend to keep our solar blanket on, even during the day if no one is using the pool. The last test was
CYA 30
FC 5
CC .2
alk was 180
pH 7.6,

but that was about 2.5 weeks ago. I have dropped the SWG to 20% and I am planning to bring the water in for test tomorrow. Never thought i may have to raise the pH with an SWG.

[Simmons99]

Can you post a recent - like "right now" set of test results?

Also - are you using any Tri-Chlor pucks in a floater at all? What else have you addded to the pool - anything?

Also - do you aerate the pool at all? Andy fountains, returns rippling the top of the water, a spa? If not and the cover is on a lot the pool might not be able to "out-gas" which would keep the PH from rising (Chemgeek can help you here).

[chem geek]

Yes, having your solar blanket on most of the time will virtually eliminate carbon dioxide outgassing which is usually the main cause for rising pH (so having your cover on will virtually "freeze" your pH). Your TA is high so if you use your pool and keep the cover off, you will find a reasonably strong tendency for the pH to rise. So I suggest you simply remove your cover (during the day; keep it on at night to retain heat) and you should find your pH rising.

You could also follow Ben's Lowering Your Alkalinity (http://www.poolforum.com/pf2/showthread.php?t=191) procedure to lower your TA to around 80 so that when your cover is off you won't have such a large tendency to have pH rise.

Richard

[waterbear]

Yes, having your solar blanket on most of the time will virtually eliminate carbon dioxide outgassing which is usually the main cause for rising pH (so having your cover on will virtually "freeze" your pH).
Richard, I have not found this to be true. In the colder months I keep a solar cover on my pool and spa and still have to add acid just about as freqently as when it is off. I will see if the borates make a difference this winter. I usually have to put them on around november.

Would appreciate your comments!

[chem geek]

Evan (waterbear),

Well every pool is different, but a cover should have really kept your pH much more stable. My own pool that is usually covered hardly changes pH at all now that I only use liquid chlorine, though it obviously dropped in pH and needed regular base addition when I used to use Tri-Chlor tablets.

Most of the users that report a sudden stop in their pH rise have reported using a pool cover at the time of this "freeze" in pH, so I don't know why you don't see the same thing. The borates should slow down the pH rise, but when you do eventually need to add acid, you'll have to add as much as you did before because the borates will make it just as hard to lower the pH (by adding acid) as they make it hard for it to rise. Of course, report back when this occurs and prove me wrong!

If you find that your rise in pH over time is not accompanied by a slow drop in TA, then there is some source of pure base in your system. I forgot -- is your pool plaster/gunite and when was it last redone? The curing of the cement in plaster/gunite will raise the pH and will also raise the CH though this may not be as measurable as pH. A pool cover won't do anything for this source of pH rise. Also, if you add any chemical to your pool during winter, such as a polyquat algaecide, then perhaps this is basic, though I do not know (I thought polyquat was relatively neutral).

Richard

[waterbear]

My pool is fiberglass (which I assume is non reactive) and I live in Florida so the pool is open year round. I do turn the output on my SWG down in the colder weather and shorthen the pump run time a few hours but I still had the pH rise. My alk stays pretty constant....might be from my fill water which has a TA of about 110 ppm. The only alkaline substance that goes into my pool on a regular basis is the sodium hypochlorite produced by the SWG.