Is it normal for pH and TA to slowly decline?

[BeckyL]

Hello friends,

I am considering adding borates to my pool, but my problem isn't rising pH and TA, it is that it is constantly falling.

We purchased the house last winter. Last year was a bit of a disaster, I hadn't a clue what I was doing and it took me months to get the pool clear. I wish I had come here earlier, but I did the pool store thing. The pool was leaking an inch and a half a day.

I replaced the vinyl liner this spring, have new water, no leaks, and a fresh take on how to care for it. At the end of the summer I had 8 16oz bags of Dichlor and a 40 pound tub of trichlor. I have used those to chlorinate the new water in order to get a little CYA into the mix. I've added all 8 bags and dissolved about 5 pucks using the in-line chlorinator. According to the calculations, this should have made my CYA about 20. I haven't added any stablizer. The water has been cold, the weather just got warm, so I'm adding about 2 ppm a day of liquid chlorine.

Before I start on any new addition of borates, is it normal for pH and TA to slowly decline? I only add about an inch of water a week now, but pH goes down about .2 every other day, and TA drops about 10 ppm a week. This was happening last year as well (much faster though!), but I thought it was water replacement. It hasn't rained much here near Atlanta, so I'm not sure why the drop. I was excited about borates stabilizing pH, but it seems that it helps it not RISE. I don't have that problem.

Is it normal for it to drop slowly?

Thanks in advance, and thank you!

 

[Casey]

Re: So you want to add borates to your pool--Why and How

You're pH and TA are plummeting because of your use of trichlor!!! It is very acidic. If you stop using it, you will solve the problem.

 

[BeckyL]

Ahhh... ok. Didn't know that was a side effect. Makes sense. Thank you!

 

[Casey]

Yep. It will also drive your CYA up if you're not careful. Switch to unscented bleach. You can find a lot of info in Pool School.

 

[BeckyL]

I definitely knew about the CYA side of it and have been careful with it. I was hoping to use up some of the trichlor to get my CYA up before it got warm. I still think that's a good idea, and have been counting the number of pucks I've been putting in so that I have a grasp of the CYA. Once it gets between 30-40 ppm, I will stop using trichlor altogether except when I'm on vacation.

I also only use liquid chlorine when adding each day.

So yea, I knew about CYA. I just missed the part on poolmath about the pH dropping as well (.13 ppm per puck!). I wouldn't call that "plummeting", but definitely noticeable. So now that I know that, I need to decide whether borates is something I want to get into.

Thanks again.

 

[chem geek]

For every 10 ppm FC added by Trichlor, it also increases CYA by 6.1 ppm and lowers the TA by 7.1 ppm. How much it lowers the pH depends on the TA level. At 100 ppm TA, it will drop 7.5 down to 7.15, but there's usually carbon dioxide outgassing so one may not see the pH drop by that much.