SWG is not making pH go up

[semenzato]

I have enjoyed my Pool Pilot SWG for almost a year now. It's been working great. The one feature I wish it had (but I don't think the technology exists) is a free chlorine sensor to controls the cell output level. The pool goes from periods of fairly heavy use to stretches of little use, and during the lulls the chlorine tends to build up to as much as 5-6ppm. Normally I only need 1-2ppm. It would be nice if the level could adjust itself.

Anyway, there is one thing that puzzles me. In almost a year of use, I haven't had to add any acid yet. The pH was at about 7.6 when I started using the SWG and it's stayed there the whole time. I even tried a different testing kit to make sure there wasn't a problem with mine.

The pool is about 10,000 gallons and I run the pump about 4 hours/day, a little more in the summer. The cell output level is set at about 20-30%. I stabilized the pH with a fair amount of borax (a couple of boxes I think, but I don't remember). It's an indoor pool so it gets no leaves or other junk and as I mentioned the chlorine level doesn't need to be very high. Still, I haven't noticed *any* pH increase. (It's not going down either).

Did anybody have this happen to them? I am puzzled and even a little worried.

Thanks!
Luigi

[chem geek]

Luigi,

What is your TA level and your CYA level? A low TA (adjusted for CYA) could help explain your lack of pH rise. Either that or your SWG has somehow figured out how to output hydrogen gas bubbles without pulling out the carbon dioxide from your water!

You've probably got a fair amount of Borates in your pool. Two boxes of 20 Mule Team Borax (each is 72 ounces) would give you about 17 ppm Borates (measured as Boron) in your 10,000 gallon pool. That might be enough to act as an algaecide and that helps to cut down the amount of chlorine that gets used up fighting algae. So your lower cell output level means less hydrogen bubbles so less pH rise, but it is unusual to see no rise at all unless your TA is low.

Just to make sure, are you adding any chemicals to your pool on a regular basis such as non-chlorine shock or anything like that?

Richard

[waterbear]

I would attribute it to the borax. Since I have brought my borates up to 50 ppm I have used so little acid in my pool and my pH just stays at 7.6!

[semenzato]

Thank you for the replies. I haven't measured TA for about a year. At the time it was in the desired range but barely. I can't remember if it was at the high end or the low end. I assumed it would not change.

I changed the pool water shortly before I added the SWG so the CYA from the dichlor is very low. I remember measuring it. The pool gets little or no sunlight so that works.

It's probably the borax then. So that will work fine for a while, but when I finally will have to add acid, I suppose I will have to add a lot!

I am wondering if there is something leaking into the loop that is providing the negative ions while slowly dissolving some important part of the pool :-|

[chem geek]

It is partly true that the Borax will buffer the pH so that when you do add acid you will be adding more than if the Borax were not there, but as waterbear points out there are reasons why the total amount of acid needed will be lower. Borax has a double-effect -- it's both a pH buffer AND an algaecide and the latter allows for less chlorine and less chlorine means less SWG on-time and less pressure on making pH rise.

Your TA will eventually drift downward and the pH will slowly drift upward. Anyway, if you CAN test your TA (and CYA level, if you can, though TA is more important), that would be helpful -- not to solve any problem, since there isn't any, but to help confirm or refute what I believe is going on. I always want to compare the "theory" against real-world behavior.

Thanks,
Richard

[semenzato]

It is partly true that the Borax will buffer the pH so that when you do add acid you will be adding more than if the Borax were not there, but as waterbear points out there are reasons why the total amount of acid needed will be lower. Borax has a double-effect -- it's both a pH buffer AND an algaecide and the latter allows for less chlorine and less chlorine means less SWG on-time and less pressure on making pH rise.

Your TA will eventually drift downward and the pH will slowly drift upward. Anyway, if you CAN test your TA (and CYA level, if you can, though TA is more important), that would be helpful -- not to solve any problem, since there isn't any, but to help confirm or refute what I believe is going on. I always want to compare the "theory" against real-world behavior.

Thanks,
Richard

Thank you and sorry it took me so long, but I finally got around to measuring the alkalinity and it seems fairly normal at 140 ppm.

[chem geek]

Wow, that's actually high (for SWG pools) so that must mean that the Borax is REALLY potent for cutting down the pH rise (and that's what waterbear sees as well). It may also be that the very still air in an indoor pool helps so the aeration may be very, very low. It's interesting, in any case. Thanks a lot for the update!

Richard

[semenzato]

The pool is almost always covered with a solar blanket (bubble wrap). This is a necessity or the humidity in the room would be unbearable. I suppose this could prevent the hydrogen from being released, and perhaps it forms bubbles under the cover which are readsorbed in time?

Thanks!
Luigi

[chem geek]

Maybe. But others with covers still experience a rise, but those are outdoor pools. Maybe your bubble pack is different and as you say it keeps a layer of higher concentration carbon dioxide under it, but the gas does have to go somewhere in any event.

Another reason you probably don't see as much rise is that as an indoor pool your SWG is running far lower than in an outdoor pool because there is no sunlight to breakdown the chlorine. This is partly why we think the Borates also help -- not only as a pH buffer, but also as an algaecide to lower the production of chlorine. When waterbear added Borates, he found he could lower the output of the SWG.

Anyway, lots of reasons -- don't know which ones are most important -- but it's good news at any rate. We do know that we have at least two solutions that both work and work even better together -- lower TA and use of Borates. That's good enough for now.

Richard

[steveinaz]

I've noticed the same thing since my SWCG was fired up. PH seems to be stable for much longer. Where I used to add about 2 cups of muriatic every 3 days, I'm now only adding 1 cup a week.