ph keeps falling

[ljh]

Have been doing BBB for 3 years (bought my first place with a pool and found this forum-thank you very much), so the water is always clear, no algea or other problems. But I can't keep the ph stable. I have to put in a 4lb box of Borax every week. Is this exessive? Here are the facts:
25,000 vinyl in-ground, solar cover on most of the time (when I'm at work)
CYA 30
FC 3 - 5 ppm (I check and adjust daily, don't let it drop below 3)
pool temp 78 (it's been warm this week - had been around 74 for the past month or so)
ph 7.2 (I'll put in a 4 lb box and it will go up to 7.6, but will drift down within a week) I don't let it go down below 7.2 but I can't get it to stay up. We've had no rain so why won't it stay?

[JohnT]

What is your total alkalinity? That's usually the key to stable pH.

[ljh]

TA is 110, this is in the right range, correct?

[rilesworld]

I had a similar phenomenon earlier this year, and I'm not sure I ever found an explanation for it. I did raise my TA a little bit, to a little lower than you have it now. That didn't seem to have much effect. The only thing I could think of was that we were getting a lot of leaves, pollen, etc. in the pool and that might contributing to the lowering of the Ph.

For us this lasted about a month or so and then just stabilized. The extra debris in the pool was the only thing I could think of unless some of the big showers was adding acid to the pool, which is possible, but it seemed as though my Ph would drop whether we had rain or not. It has now been a consistent 7.6 for several months.

Riles

[Watermom]

TA is 110, this is in the right range, correct?

110 is a good level for TA.

[KurtV]

TA is 110, this is in the right range, correct?

Yes, but unless your calcium level is too high you can probably raise it a good bit without it causing any problems and raising your TA will help keep your pH up.

An alternative is to aerate your water somehow. That will also raise, or at least keep steady or slow the fall of, your pH. Do you have any water features or fountains that you could use for aeration?

What is the calcium hardness of your water?

[KurtV]

Another thing that will probably help keep your pH up is removing your solar cover more (though that may not be a good option in your northern clime). That may allow more CO2 outgassing which will raise your pH.

[chem geek]

ljh,

It's very, very strange to have the pH dropping so consistently in a BBB pool. A rise would be understandable, especially if the pool were uncovered, but a drop even with the pool covered is unusual.

Is there anything else you are adding to the pool that might be acidic? With BBB you are obviously not adding Trichlor or Dichlor. Are you adding any CYA? How about non-chlorine shock? Algaecide? Any chemicals other than bleach or chlorinating liquid and the Borax?

Do you have any evidence of scaling or is your Calcium Hardness really high?

Have you had lots of rain (and I mean LOTS as in many inches)?

Richard

[ljh]

I haven't checked for CH as it's a vinyl pool and didn't think I needed to do that. Should I get that number - would that be helpful?
No large amounts of rain, nothing extra added to the pool (keep it simple). No algaesides recently (I put in some at spring start up in May). I need to keep the solar cover on or there is no swimming at all till August - very large shade tree in back yard (which was probably much, much smaller when the pool was originally installed in 1971!) There isn't a lot of debris in the pool (thanks to the solar cover) and I clean it every day (I'm obsessive -what can I say - a sparkling pool is a thing of beauty). I thought reading somewhere (before the infamous crash) that some pools have a natural ph and one shouldn't fight it. I haven't let the pool go to see if it bottoms out somewhere (it's that obsessive thing again - drops below 7.6 and I'm in there with the borax!)

[ljh]

Opps, I lied (well, forgot actually) I added DE to my sand filter this week as it has been suggested on a thread else where that this will "polish" the water (did I mention the sparkling water obsession?). But the ph thing was happening before that, so I don't think that's it.
The CH is 110 (again I think this is in the acceptable range - though I have a vinyl pool, and no heater, so it shouldn't matter).
I did recheck the TA and now it is 80! Would adding the DE affect the TA? I had checked the TA several times since opening in May and it had alway been 100-110 so this is new.
I have no water feature so the only aeration option I have is turning the return nozzle to the surface (would that help?). I've seen add on fountains (seems to hook into the return) at the pool store - do I need an excuse for a new pool toy?
Thanks for all your suggestions