raising a stubbornly low pH

[wilcfr]

Here are the particulars:

gunnite inground pool
38,000 gallons
TA 119
Chlorine 3ppm
Calcium 240
pH 7.01
Temperature 87

I test chlorine(dpd), TA(titration) and hardness(titration) with Hach Kit water testing kits and pH and TDS with handheld meters

We had to add a good bit of dry acid to get our TA down from 300 to 119. This was done over a period of 2 weeks. The pH dropped to 6.67. We added 4 boxes of Borax, which over the course of a week only brought the pH up to 6.8(we have been using the Borax for a couple of years and don't seem to have the luck with it many of you on this site have). We have since added 10 lbs of soda ash over a period of 3 days and gotten the pH up only to the 7.01 level. From what I have read on this forum and website the Borax should have raised the pH considerably more than it did, and based on a number of online pool chemistry calculators the 10 pounds of SA should have raised our pH to around 7.3-7.4. We use 3 inch trichlor in an automatic chlorinator and shock with either calcium hypochlorite or sodium hypochlorite. The pool as been shocked once using the calcium hypochlorite. Any suggestions as to how best to raise the pH another 2-3 points without blowing the TA out of wack again? And any guess as to how long it should take? The pool is clear and swimmable, but I would really like to get the pH up for a variety of well accepted reasons. We always battle the TA problem early in the season, last year it took 4 weeks, a lot of acid and a subsequent drop of pH down to 5.5 to get it down from over 300 to a reasonable 190.

Thanks

[waterbear]

First, trichlor is very acidic and will cause your pH to go down and your CYA to rise as you use it.

Did you airate when you lowered your TA? See this thread for the procedure
http://www.poolforum.com/pf2/showthread.php?t=191
This is what you should do if you have not.

By just lowering the pH with all the acid you dumped in you probably have not really lowered the TA but just shifted the amount of carbonates/bicarbonates/carbonic acid buffer system that we call TA in the water to less of the carbonates/bicarbonates and more carbonic acid (which is just carbon dioxide dissolved in the water (which does not register on the test for TA, it only measures the carbonates and bicarbonates). If you start airating the water your pH will rise and your TA will come down a bit (at 119ppm that will not be a problem) by actually driving out some of the carbon dioxide that is dissolved in the water. This will lower the TA because NOW you have actually lowered the amount of the carbonic acid/carbonates/bicabonates in the water, which is what you want.

The TA is a buffer system that keeps the pH from changing. That is why it might seem that you have to use a lot of Borax or acid to make changes. You wlll put a bunch in and nothing seems to happen. You will finally reach a point where you have overcome the buffer and the pH will start to change and it might take a lot more than you think.

The trichlor is constantly lowering your pH. If you use Soda Ash to correct this you will be raising you TA along with your pH and get into an endless cycle. You will make your pool even more resistant to pH changes. Borax is your best bet because it has a minimal impact on TA.

Calcualtors can only give you an approximation of how much acid or alkaline material will lower or raise the pH. If the buffer system in the pool is high the pool will be more resistant to pH change and want to stay where it is so they can give you a starting point and nothing more in many cases.

I noticed that you did not post any numbers for CYA (stabilizer). I am wondering at what level it is at since you use trichlor and that is constantly causing your CYA level to rise. 3 ppm FC is fine if your CYA is exremely low but but if it is anywhere above about 50 ppm you should be running your FC higher to compensate. See this post
http://www.poolforum.com/pf2/showthread.php?t=365

If your CYA levels are very high you might want to consider a partial water replacement which will not only lower the CYA but also the amount of sulfates in your water from the use of dry acid.

Hope this has been helpful.

[wilcfr]

New readings as of this morning
pH 7.06
TA 136
FC 1.7
TC 2.6

Actually our CYA is low, below 20, thanks for asking. We have not aerated yet this season. Last summer we bought a hokey little float around fountain that hooked up to our inlets that did a fair job of that(sadly we don't have any 10 y/o boys at our disposal, just an 8 y/o Springer).

About Chlorine. We have an auto chlorinator that uses the 3 inch tabs of trichlor. It would seem that is not considered a good way to go. We have also used granulated dichlor in the past when our auto was broken. I know that dichlor is also stabilized, but don't know its affect on pH. Obviously liquid bleach is cheap and has a high pH (around 12 if I remember correctly) and is easy to use, but is it stable enough if our CYA is low? What about just throwing in a 1 lbs bag of Cal Hypo( another high pH product) every 2-3 days, accepting days of heavy party use, which is maybe twice a year? For the most part the pool is used daily, weather permitting, be my wife, me and our aforementioned Springer who actually enjoys it more than we do.

Thanks for the reply. We will try to find some 10 y/o boys or hook up the fountain again.

[aylad]

The trichlor isn't necessarily "not a good way to go", unless it is causing you problems. For most people, that problem would be a huge rise in CYA levels. For you, it appears the problem is consistently having to battle low pH. If you would aerate your water and stop using the trichlor, I bet your pH problem will clear up quickly. You could switch to cal-hypo or bleach either one in the meantime.

Janet

[duraleigh]

You're getting very accurate advice from some sharp cookies.

You might consider shocking your pool. I notice some CC in your results and it might be a good idea to clear it up.

I LOVE Cal Hypo....only drawback is it will slowly increase your CH, which looks high enough already.

Your CYA level will have the same affect on bleach as it does Cal Hypo....you'll lose some of it. I lose about 2-3ppm per day running CYA of 35 or so. I'm upping mine to 50 to try and retain a little more chlorine during the day.

I'll bet Janet's right on the money. If you don't use trichlor, your pH issue will soon be obsolete.

[wilcfr]

Thanks for all the advice. We were not able to find any 10 y/o boys, but were able to play with the direction of the inlet discharge to get a nice little aeration going. Over the course of the last 24 hours our TA has dropped to 102 and our pH is up to 7.38. I added 2 lbs of Cal-hypo this moring because our FC to TC was still a little off. I will probably continue to use the Trichlor in the auto chlorinator on a low setting to help stabilize the granular and liquid Cl and augment with the CH granules or SH liquid to keep the chlorine level where it should be.

I have to say that the internet is a wonderful thing. I am a member of probably 15 forums some as an "expert", a few as a "little knowledge is a dangerous thing member" and a few more as a "newbie", but it is a wonderful vehicle for sharing info and experiences. Thanks again for the advice.