Question regarding PH

[david8956]

First of all, new here but not new to pool care. I just recently found this fantastic site and got all excited about pool care again! I'll be going to the BBB method after I have had time to re-read everything a couple of times, but I do have a question about PH now.

I recently installed a salt generator (Aqua-Rite) for my 14K gallon in-ground pool, set at 60%. In the past when I used chlorine tablets in the auto chlorinator my PH was pretty steady all the time, but now that I have started using the SG I have to add about 1/2 gallon of muriatic acid every week to keep the PH down, is this normal? It seems like I am spending as much for acid as I used to for chlorine tablets(?) I don't remember seeing this "side effect" of a SG when I was reading up on them, but maybe I missed something........

Thanks for your help....there is a LOT of good info on this forum.

 

[dmanb2b]

Welcome to TFP....yup, depending on where your TA is, SWG can lead to a rise in PH. The solution would be to lower your TA to around 70-80 and see if that helps.

The lowering TA sticky is in pool school (button on to right of page) and depending on how high your TA is now, could take a few gallons of MA and 2-3 day of aeration to get it down...but once lowered your acid demand will drop considerably. The reason it was steading in the past is that Trichlor tablets are acidic.

 

[svenpup]

It is normal. An SWG tends to push up on pH as opposed to trichlor which is net acidic. TA also tends to push up on pH. You may be able to adjust your TA lower to reach a more stable level. Regular additions of MA will tend to bring your TA down slowly anyway.

Post a full set of numbers and we can give more specific advice:

FC
CC
pH
TA
CH
CYA

Also, it is helpful if you put your pool info in your signature (type, size, etc).

 

[mickey4paws]

Welcome to the forum How long are you running your pump? I run my pump for about 11 hours, but have my SWG set for 15%. I believe, and I could be wrong, that the less time the SWG has to generate chlorine, the less outgassing there is, and thus less PH rise. I ran my pool like this all last summer and only had to add acid 2 times all season.

Also, if you have not already ordered one, I highly recommend the TF100 test kit (links are all over this site for it)

 

[david8956]

I knew I could find the answer here, time to turn on the waterfalls and add acid :-D

As asked for, my current numbers:

FC: 3.0 ppm
CC: No idea, I REALLY need to order a TF100
PH: 8.0
TA: 125 ppm
CH: 260 ppm
CYA: 100 ppm

As you can see, thanks to the help from you guys I realized if I lower my TA I shouldn't use as much MA every week.

Also, my pump runs 8 hours per day.


Thanks!

 

[waste]

David, welcome to TFP!!

I predict a soon to be trouble free pool for you and a great future here

It's my speculation that the concentration of the hydrogen bubbles plays a large roll in the pH upswing - on the pools I install, we put ~ 10 returns in and I haven't seen the pH rise associated with SWCGs, but then I make sure to keep the TA <100 - on pools with only 1 or 2 returns, the pH creep does occur. The only way I can explain this is that on the ones we build only 10% of the hydrogen bubbles are coming through each return while on the other pools the return(s) have 50 or 100% of the hydrogen being introduced to the pool in one place :blah: (just a little report from the field )

 

[flintstone]

You may want to drop your CYA level to 80. With a reading of 100, you will have to keep FC at a minimum of 5.0 to maintain minimum sanitation levels. In order to do that, you would need to crank up the SWG to even higher than current levels.

Since the only way to reduce CYA is to drain, you may want to do that before adding anything else.

Having an SWG and waterfalls means you will be adding Muriatic Acid, except perhaps during the winter.

Your SWG setting at 60% seems really high. I have never gone above 25%. I'd figure out that one before anything else.

 

[david8956]

I think my 60% setting is due to me almost being undersized as far as cell size.

My pool is actually 13,700 gal according to the builder. I purchased the 15K gallon cell on advice I received (Very light load......pool only gets used by 2 people a couple of times a week......pool is screened in, etc). I assumed this is why I am running at 60% (@ 8 hrs per day)

And for those that are familiar with central Florida thunderstorms in summer.................my CYA will be coming down pretty quickly before long now that I have stopped using chlorine tablets. It's not unusual to get 3"-4" of rain a couple of times a week here.

 

[JasonLion]

You need to be careful with a CYA reading of 100. The common CYA tests will tend to report CYA levels over 100 as if they were 100. So your CYA level might actually be higher than you think it is. You might want to try mixing equal amounts of pool water and tap water and then testing the CYA level of that. If that comes out around 50, then your CYA level really is around 100, but if it comes out higher than 50 you will absolutely need to get the CYA level down.