New Pool Alkalinity and PH

[Naplespool]

I've been lurking here for about a year and have finally joined. This seems to me to be the best pool forum on the web. Well done!

I live in Naples, FL and finished a new plaster pool in Naples. It's an 8 x 50 swim lane with a 6 x 16 sun shelf and hot tub. It holds 17,250 gallons of water and has a surface area of about 665 sq-ft. and has a SWCG.

The fill water in Naples seems to have a PH of 8 or so, a TA of about 40 and CH of around 50. I use a Taylor FAS-DPD test kit and use your great Pool Math for calculating the CSI. We keep the pool around 84F. Over the last week, the pool has been using about 1/4" of water per day which is about 100 gallons of new fill water per day, if I've done the math right: 665/12/4 cu-ft*7.5 gal/cu-ft.

SWCG set at 55% (IC40), pump running 10 hrs at 2100 rpm so chlorine use is about 2 ppm/day.

Current Chemistry
FC: 5 ppm
PH: 7.8
TA: 80 ppm
CH: 400 ppm
CYA:70-80 ppm
Boric Acid: 50 ppm

At the above numbers, Pool Math says computes a CSI of +0.06 to -0.21 for a PH range of 8.0 to 7.6. Currently it seems to take about 3-4 quarts of MA per week to keep PH in that range. I am testing chemistry daily because when I leave Florida at the end of April I'd like to leave clear chemistry targets for the pool company, with an idea of how much Acid the pool will use and how much of each chemical for a 10 ppm adjustment.

My questions are about acid consumption and TA. Before adding the Boric Acid I worked for a week to get the TA down to about 60-70 but the TA now seems stable at 80 after the Boric. Fill water and MA are the only chemicals I'm adding, other than the effect of the SWCG.

--Should I try to bring TA down further to reduce the amount of Acid the pool requires? (That would shift my CSI.)

--As I add Acid, week by week, will the TA drop also? I'm unclear if small quantities of Acid will reduce TA over time or whether I can only reduce TA by dropping PH to 7.0 and then aerating the water to increase PH. And if TA won't get reduce by the weekly MA addition, where is the TA coming from after the MA reduces it (set aside the fill water for the moment)?

Thanks for all the knowledge in this forum.
RB

 

[Jezza]

Welcome to the forum.

Adding acid will bring the TA down at the same time that it brings pH down. With new plaster and a SWG you can expect that pH will rise faster than it might do otherwise and so you may be adding acid frequently for the moment. This will probably keep your TA down without too much extra effort and help to stabilise your pH. TA can really only be added to the pool chemically ( i.e.- baking soda) or in your fill water.

I thought I might also mention that your FC is a touch low for your CYA and go easily under the minimum when algae could set it. I would try and work it up to 7-8 FC and give yourself some wriggle room.

 

[Naplespool]

Thanks for the comments on TA. I've been wondering about that for a while. Pool Math indicates 4 ppm is minimum and the TFP recommendations suggest a range of 4-6 for CYA of 70-80 so I thought 5 ppm was center of the range. I'll boost it.

A concern is about the off-season where I only get chemistry checked once a week. Will it be a problem to have them add a week's worth of acid (~3 quarts), dropping the PH from maybe 8 to about 7.3?

 

[Jimrahbe]

N,

SWCG pools tend to like the pH at about 7.8. Mine will stay at 7.8 for several weeks. If I try to maintain 7.3 or so, it will almost immediately climb back up.

Are you running your water features and spa spillover on a constant basis? If so this will also increase your pH.

Thanks for posting,

Jim R.

 

[Naplespool]

Jim, Our spa has about a 2" spillover and I bleed only enough water through to keep it full. Then at night I run it for an hour with no spillover but I notice it does draw some air into the returns, even at a low pump speed.

- - - Updated - - -

And I should also add that I'm finding it challenging to read the difference between 7.8, 7.9 and 8.0 so I'm probably adding acid before I get to 8.0.