Reduce PH Auto Fill Water

[BPet]

I have a large recirculating fountain that has an auto fill device and it is connected to one of my pool return lines . This insures that the fountain always has the proper amount of water and I do not have to treat the fountain for algae etc. It draws approx. 30 gallons/day from the pool water. The swimming pool has an auto-fill connected to the side of the house and since the pool level always looks good - it must be getting approx. 30 gallons/day of tap water.

The Issue: I have to add about 1+ gallon/week of acid to the pool to keep the PH around 7.6-7.8. I tested the Tap water and the PH is higher than the 8.2 of the test kit. I'm thinking that the added high PH tap water is raising my pool PH? Is there any type of filter device that I could add to my pool auto-fill line that would reduce the PH before it gets to the pool? I have read online that Brita filters lower PH to 6 (source: google) and I wonder if anyone here has any other suggestions? Pool is approx. 18,000 gallons. I would rather not automate Acid since it is so hazardous...

Thanks!

 

[domct203]

Hello,

I would imagine that the volume of fill water in comparison to the volume of your pool would be negligible in raising your pH, and that your pH rise is due to other issues (aeration, high TA, etc).

pH rise in a pool is not uncommon at all.

How do you test your pool, and how often?

210 gallons (30x7) of fill water in an 18000 gallon pool is only about 1% of the total volume.

Dom

 

[duraleigh]

I have read online that Brita filters lower PH to 6 (source: google)

I am not sure how that would work....do you have a link? Did they mention capacity?

 

[Cinic]

What's the TA of the pool and fill water?

 

[BPet]

I use the TF Test Kit and I have a Pentair SWG. I do a complete test once a week and I check the chlorine and PH every 2 days because I'm trying to get the PH stable - the pool is 2 months old. Today's test results:
PH - 7.5
FC - 6.5
TA - 50 (please read below)
CYA - 65
CH - 350 (this was 325 before I started adding Sodium Bicarb)
Salt - 3200

I have 3 Bobe' 12" Wide Copper Scuppers and so they aerate the water a lot

Ta:
9/17 - 60 - added 42 oz Sodium Bicarb (from Home Depot "Total Alkalinity Increaser" - 100% Sodium Bicarb)
9/24 - 60 - Not sure why it did not go up since last week? - Added 32 oz Sodium Bicarb
10/1 - 50 - (tested twice) What is going on? it is like the Sodium Bicarb is reducing my TA?

I have been adding approx. 1 Gal Acid per week.

My Tap Water:
TA - 60
PH - 8.2+(my test scale maxed out at 8.2)

What are the odds that the "Total Alkalinity Increaser" was mis-packaged and its an Alkalinity Reducer? I'm afraid to add more for fear of lowering TA further...Should I just get a new bag from another brand? - although now I'm getting concerned that if I keep adding Sodium Bicarb, my Calcium Hardness is going to get too high?

Thanks,
Brett

- - - Updated - - -

Dom, Good Point on the volume, maybe the tap water is not the issue...

 

[BPet]

I am not sure how that would work....do you have a link? Did they mention capacity?

Maybe this is not my issue due to the volume compared to the pool, but here is what I found online in case your curious:
How to lower ph via brita filter - YouTube
Brita Filter Water Analysis... Tested LIVE For pH, TDS, And Potentially Harmful Contaminants - YouTube (he indicates it produces PH 6.3, but later PH rises?)
Dave, do you think I should keep adding Sodium Bicarb or will that make my Calcium Hardness to high? Thanks again!

 

[YippeeSkippy]

All that acid is most likely causing the TA to drop. That your pool is only two months old (plaster, I take it?) is also common as the plaster cures for the pH to require acid. Assuming all continues well this may go on for months before leveling out.

 

[BPet]

All that acid is most likely causing the TA to drop. That your pool is only two months old (plaster, I take it?) is also common as the plaster cures for the pH to require acid. Assuming all continues well this may go on for months before leveling out.

Should I be worried about increasing the Calcium Hardness by adding more Sodium Bicarb?

 

[wjr75]

If you have new plaster that is probably the cause. When I had my new Pebble Sheen applied a year ago it took 6 gallons of MA in 4 months to keep the ph in range.

 

[duraleigh]

Should I be worried about increasing the Calcium Hardness by adding more Sodium Bicarb?

I am not aware there is a relationship. Am I overlooking something?

 

[chem geek]

Are you using full-strength Muriatic Acid (31.45% Hydrochloric Acid)? If so, then one gallon in 18,000 gallons of pool water will lower the TA by 28 ppm which is substantial. 42+32=74 ounces weight of sodium bicarbonate should have increased the TA by 18 ppm but given the amount of acid you've been adding the net result over one week week would be 18-28 = -10 ppm so a 10 ppm drop in TA. So what you are seeing is not surprising at all. Basically, to maintain the TA level you'd have to add a lot more bicarb given the amount of acid you've been adding. In effect by adding acid+bicarb you are adding carbon dioxide back into your pool (and adding salt as well):

HCl + NaHCO₃ ---> CO₂ + H₂O + NaCl
Hydrochloric acid + Sodium Bicarbonate ---> Carbon Dioxide + Water + Salt

However, this acid+bicarb vicious cycle needs to be broken. If the recirculating fountain is primarily recirculating its own water and is truly only taking 30 gallons/day from the pool so that is all the fill water that is then getting into your pool, then that isn't enough to be causing the pH rise. It does seem that the pH rise if from a combination of the new plaster and the aeration of your pool water from the scuppers.

I have 3 Bobe' 12" Wide Copper Scuppers and so they aerate the water a lot

While this aeration certainly doesn't help, the amount of aeration at the low TA level will be low. Specifically, with your numbers when the TA was at 50 ppm, the pH would stop rising completely at 7.8 if this were only from carbon dioxide outgassing. So I suspect that the new plaster is contributing and the good news is that if you don't see any rise in CH then it means that the plaster surface is hardening "in-place" as follows.

Ca(OH)₂ + CO₂(aq) ---> CaCO₃ + H₂O
Calcium Hydroxide + Carbon Dioxide ---> Calcium Carbonate + Water

In other words, such plaster hardening looks exactly the same as carbon dioxide outgassing in terms of the effects on water chemistry. The concern I have is that at your current levels your saturation index is at -0.6 and this is with fairly new plaster. Unless you have a metals problem where staining would be a risk, I'd keep your pH higher at 7.8 (i.e. lower it from 8.0 to 7.7 or 7.8, not to 7.5) and maintain your TA at around 60 ppm (keeping it lower due to your outgassing from the scuppers) and eventually as things settle down with a slower pH rise you'll want your CH to be higher closer to 400-450 so that you can maintain the lower 60 ppm TA. I would not try and keep your pH at 7.5 since that will just exacerbate the outgassing problem and risks dissolving of pool plaster (calcium carbonate).

If you aren't using 50 ppm Borates, then adding them would help slow down the rate of pH rise though they may not change the amount of acid you need to add. Why don't you try the adjustments I suggest above first to see how things go. You want your pool plaster to harden so if anything you'd want a higher saturation index to speed that up (so a higher TA), but with your scuppers that would just have the pH go up higher. Is there any way for you to (temporarily) turn off water flow through those scuppers, at least during this phase of plaster hardening?

 

[BPet]

Chem Geek, thank you so much for your detailed reply! I will aim to keep the PH at 7.8 and maintain my TA at 60ppm.

Yes, I can turn off my scuppers. How long would you guess it would take for the plaster to harden before I can turn them back on?

Thanks!

 

[tim5055]

Chem Geek, thank you so much for your detailed reply! I will aim to keep the PH at 7.8 and maintain my TA at 60ppm.

Yes, I can turn off my scuppers. How long would you guess it would take for the plaster to harden before I can turn them back on?

Thanks!

Most new plaster pool owners see pH rise for the first full year. But, as the year goes on the rise slows.

 

[Jaimslaw]

Most new plaster pool owners see pH rise for the first full year. But, as the year goes on the rise slows.

Is is true that ph rise levels will not be affected by the type of finish, e.g., a mini pebble finish or even a micro pebble,finish? At first blush, one might think its possible the given the ratio of aggregate to plaster, there could be a difference in ph rise levels, tho me thinks this is not the case.