ph keeps falling

[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

[Watermom]

I don't know about whether or not the DE would affect your ph or not. But, if your TA is 80 and you are having lots of ph bounce as you are, I would bump it back up with some baking soda.

[chem geek]

ljh,

With a vinyl pool, your CH is fine and I was looking for CH that was too high anyway so your pool's CH level doesn't explain the pH drop.

As for a pool's natural tendency towards a pH, that usually refers to a directional push based on chemical additions plus outgassing of carbon dioxide. So with Trichlor pools, the tendency is for lower pH and generally a base (Borax or pH Up / Washing Soda / Sodium Carbonate) needs to be added. For hypochlorite pools (bleach, chlorinating liquid) the tendency is neutral or rising pH depending on the aeration. For SWG pools, the tendency is usually rising pH due to aeration from the SWG. The degree varies based on the amount of aeration, but the direction is usually pretty consistent. For these latter pools with a tendency to rise in pH, the rise slows down at higher pH so appears to slow or stop at a higher pH (i.e. to reach a natural pH), but this is consistent with outgassing based on this table (moving from left to right).

The TA drop would be consistent with some sort of acid getting introduced into your pool combined with some degree of outgassing (assuming the pH was the same each time you measured the TA -- if the pH was lower, then a somewhat lower TA would be expected, though not a 20-30 drop). I wouldn't think DE would do that.

With a solar cover on, you are keeping the outgassing to a minimum so there is probably very little upward push on pH so that is understandable. The mystery is what is causing the pH to drift downward. 4 pounds of Borax at a TA of 100 (CYA of 30) should cause the pH to go from 7.2 to 7.4, not 7.6, but that could just be measurement error on both ends of the pH measurement. At a TA of 80, 4 pounds goes from 7.2 to 7.5 which is closer to what you are seeing.

Going from 7.6 to 7.2 in a week is like having the equivalent of 40 ounces of Muriatic Acid added to your pool. It is just very, very odd.

Increasing your TA will reduce the amount of pH drop per week, but won't change the amount of Borax you need to add. The carbonate buffer gets stronger at lower pH so dropping from 7.6 to 7.2 in one week would go to just below 7.0 the following week (i.e. it wouldn't go to 6.8). Nevertheless, with your vinyl liner you don't want the pH to get too low (i.e. below 7.0) so you do have to stay on top of this each week.

If you do aeration, then you can keep the pH more stable, BUT you'll have to add Baking Soda periodically to maintain the TA. If you aerated enough to compensate for the equivalent of 40 fluid ounces of acid per week, you would lose about 7 ppm TA every week and need to outgas slightly less and add 36 ounces weight of Baking Soda per week.

I think we need to figure out the source of the "acid". By any chance, this isn't a new liner, is it? Though we know that new plaster cures and causes a significant rise in pH, I've never heard of new vinyl doing the opposite, but I'm open for any suggestion at this point.

You say you check the chlorine daily, but what sort of chlorine consumption do you have at your 3-5 ppm FC level? With a cover and the lower temps, you shouldn't be having much consumption at all -- if it's more than 0.5 ppm FC or so then something is consuming chlorine and maybe that something is producing acid (though that's a heck of a lot of acid). Maybe the cover, since it's a solar cover, is letting UV rays through and that would lead to higher chlorine consumption. My cover is fairly opaque (it's an electric safety cover) so my chlorine consumption is very, very low when it's kept covered.

Richard

[ljh]

added baking soda today - will check the numbers tomorrow morning. the liner is 4-5 years old so I don't think that is it. I usually lose 2-3 ppm chlorine a day, even with the cover on. Depends on how sunny it is and how warm the water is- I have the clear bubble wrap type liner. The water is clear and there is never a lot of CC when I check - usually .5. I thought I was consuming a lot of chlorine because of the ph drift or low CYA....or is a that normal? I usually add the chlorine at night when the sun goes down so the chlorine gets to do some work (very light bather load, by the way, just me and a few friends, once or twice a week, not any splash out to speak of) and I check in the morning before I go to work to make sure it's between 3-5, and then I check when I get home at night to see how much to add that night. If it's cool or cloudy I may skip that day - and so far it's never been below 2-3, (Had algae the first summer - I am never fighting that battle again!) Does that seem normal or too much chlorine loss per day?

[chem geek]

It sounds like the cover lets UV through -- at least some. That would explain the variation on sunny vs. cloudy days. See if you can check the loss overnight. So add chlorine at night with the pump running, wait at least 30 minutes or up to an hour, then check FC levels (you can then turn off the pump if you don't normally run it at night). In the morning, turn on the pump if it hasn't already started, wait at least 15 minutes, then check the FC level (early in the morning before the sun gets too high in the sky. What is the FC drop? That will tell you if you've got something consuming chlorine other than sunlight.

The loss is normal if the cover lets UV through so let's assume that's the case. The overnight (non-sun) loss is really the key so let's see what that is before jumping to conclusions.

The pH drop is still a mystery. Though you have little splash-out, check the pH of the fill water just in case (maybe there's a leak in the pool -- doubtful though).

Richard

[ljh]

Alk is now up to 100, will try testing for CL at night and again in morning and post results, thanks for the suggestion