Constant pH Rise

[Mikie]

After a complete pool refill, and aswitch to BBB with 50 ppm borates (20 Mule Team Borax), I find that I need to add acid every day in order to keep the pH below 7.8.

Here are this morning's numbers:

FC 4
TC 4
pH 7.8
TA 75
Borates 50
CH 210
CYA 45

The pool has a spillover spa, which contributes to the pH rise, but I did not have this issue before. I am adding at least a pint of acid a day in order to bring the pH down to 7.6. I expected increased acid use with BBB, but given my reasonably low TA and 50ppm of borates, I didn't expect to be adding nearly this much.

I should add that the water looks great, and was shocked pretty hard after the refill, so I doubt that I have a bunch of bacteria lurking around. FC consumption is about 1 to 1.5 ppm per day. Combined chlorine has never tested positive.

Should I expect to be adding this much acid? If this trend continues, I'll be spending much more on chemicals than I did with trichlor.

Thoughts?

 

[frustratedpoolmom]

How old is your pool?

 

[Mikie]

4 years old

 

[frustratedpoolmom]

I should have said Welcome first!

Well that rules out new plaster as the cause.....

How are you testing your water (strips, drop based kit?)

 

[Guest]

Are you waiting for the pH to rise to 7.8 before adding acid? The borates pretty much keep the pH right at 7.7 so if you are trying to keep it at 7.6 you will find it difficult. Also, I would drop the TA a bit lower, perhaps to 60 ppm and increase the CH to keep the water balanced to help compensate for the spillover's aeration.

Also, what is the pH and TA of your fill water since you have an autofill.

Actually, at a pH of 7.8 you have a calcium saturation index of -.16 at 75 degrees and -.08 at 85 degrees so I would leave the pool at 7.8 in your case and lower it to 7.6 when it climbs above that! Those saturation numbers are exactly what you want! (at pH 7.6 they run from -.32 to -.23 which is still fine but your saturation index is actually better at the higher pH for your pool.

 

[JasonLion]

Do you run the waterfall and/or spillover most of the time? The more aeration there is, the more upward PH drift you will have.

 

[Mikie]

I'm using a taylor FAS DPD kit and I've verified the pH readings at 2 pool supply stores. The refill was about a month ago.

The spillover is running all the time (6 hrs ad ay right now) as there is no other way to circulate filtered water to the spa. About 20% of the recirculated water is running through the spa. I realize this contributes to the rising pH, but I had no drift before the refill, with TA=110, CH=450, and CYA too high to measure.

 

[Guest]

I just edited my previous post and added some new info so you might want to reread it.

I suspect that you never really needed acid before but used a lot of baking soda to keep up your TA since the constant addition of acid from the trichlor and the constant aeration was constantly lowering your TA. Muriatic acid is not expensive and what you will save in the long run from not needing algaecides or to drain a refill or have a pool go green for 'no apparant reason' is going to be a lot of money .

 

[Mikie]

Yes, I wait until the pH gets to 7.8 before adding the acid, unfortunately, this is pretty much every day. I'm adding an average of 24 oz of 6% bleach a day to keep the FC ~ 3-4

I'll try increasing the CH a bit, say to 250, but I was trying to keep it on the low side since I had calcium scale problems before the refill. The waterline tile is natural stone, which is hard to clean, so I'm not too excited about dealing with that again. This contributed to my desire to keep the pH at 7.6, and the CSI a bit on the low side.

The TA is slowing dropping from the frequent additions of acid, it was at 85 a week ago, so I'm not sure intentionally lowering it is needed, unless my pH related acid consumption drops.

I'll raise the CH a bit, and see where the pH wants to go without adding acid for a few days. If it hangs around 7.8 with a lower acid demand, I'll let it sit there as you suggested. Make sense?

 

[Mikie]

Before the refill, with triclor, I did not have to adjust TA or PH more than once every couple of months. TA of fill water is about 60, but the autofill is on vacation since there has been very little evap since the refill