Frustrated with low pH

[doughboy]

This season my pH has been low and I've been unable to bring it up. Pool Calc says I need 1-2 boxes of borax. However I have already added 4 boxes of Borax in the past month with no longterm effect. The highest pH reading I've seen is 7.2, but it slips back down after about a week. Do I keep dumping in borax or should I do something different?

I have a 12,000 gallon fiberglass pool with a sand filter, gas heater, automatic cover, and Baracuda G3 in Indiana. I use bleach for opening or big changes, trichlor for ongoing maintenance (primary), and dichlor powder (rarely). I've used baking soda and muriatic as needed. I've never used pool store PH UP or PH DOWN products or anything exotic.

We have had a ton of rain this spring, but the pool is always covered. I don't think significant rain is getting in the pool.

This is my third season and it's been remarkably trouble-free. Almost all I have done is add chlorine and it's been extremely stable. The water has always been crystal clear.

Using a Taylor DPD kit
TC 5
FC 5
CC 0
TA 130
PH 6.8-7.0
CYA 70 (one month old pool store measurement)

 

[JasonLion]

Welcome to TFP!

Both trichlor and dichlor are acidic and will lower the PH. You need to constantly raise the PH to compensate for that. You should increase the PH more right now, so your average PH is closer to 7.5, and then maintain things so that PH never goes below 7.2.

People who use trichlor often find that TA also falls significantly over time. It is often simpler to use washing soda/soda ash to maintain both PH and TA (though borax and baking soda will work just as well with only slightly more work).

 

[duraleigh]

doughboy,

If the CYA was at 70 a month ago, you are probably higher by now. I suggest you need to stop using tri-chlor. That will probably cure your ongoing pH issues and stop the march to big trouble with too much CYA in your pool.

 

[doughboy]

I plan to stop using trichlor and dichlor once my current supply is gone and move fully to BBB.

I've been using trichlor without driving my ph down in previous seasons. I've never had to work on raising ph before. I'm baffled by the change, but I guess the change doesn't matter. "Get a good test kit, test your water, trust your numbers, and adjust."

As for the CYA, my experience has been that my CYA drops from 70 at the start of the season to about 30 at the end. I've adusted it up at each opening and I have not seen an increase due to trichlor. I know trichlor has CYA, but it hasn't been a problem for me.

I backwash about once/week, which I know is more often than needed for the filter. My builder encouraged once/week backwash to establish a routine I wouldn't forget and to force regular water turnover. The things that build up over time (CH, CYA, TDS, etc) can be maintained effectively with the water turnover. Makes sense to me, so I've followed this advice.

I've been reading TFP (a lot) for about a year and using the calculator, but this is the first time I've posted. Thanks for the replies.

 

[chem geek]

The combination of your pool being 12,000 gallons so not too large, weekly backwashing, and using a pool cover are why the CYA doesn't build up. In particular, the use of a pool cover significantly cuts down your chlorine demand -- probably from 2 ppm FC per day down to 0.5 ppm FC per day unless you use the pool frequently.

If I use the above numbers as assumptions, then I can calculate the volume of water in backwashing that would account for the dilution. If I assume a 6-month season, then I get a rough dilution amount of 7% which is 840 gallons. That seems high for the amount of backwashing. If your pump was 60 GPM, that would be 14 minutes of backwashing. I doubt it takes that long and is probably just a few minutes, right?

Even if I assumed there was no CYA being added at all that would still be a dilution fraction of 3.2% or 384 gallons. That still seems high to me.

So you've got some other source of CYA drop or dilution. There is a slow breakdown of CYA that seems to occur even during the summer, but nothing like the drop you are seeing. Larger CYA drops are sometimes seen over the winter when a pool is "let go".

Richard

 

[doughboy]

I forgot a big source of my annual CYA drop ... winterizing the pool. I guess I drain 2,000-3,000 gallons to winterize the pool. That would account 20-25% drop in anything that accumulates.

You'll be glad to know my trichlor tablets are gone. I've got 10-12 pounds of dichlor left. I should be switched over to only bleach as a chlorine source by the end of the summer.

I'm aerating this week to lower TA. It seems to be dropping about 10/day.