Low CH reduces MA demand?

[4JawChuck]

Once I got my new liner installed and the water balanced to 7.4 and got the brown out with floc and sequestation I have been running the pool without adding any calcium to the fill water. What I have noticed is I have no PH rise even though I am caring for the pool in the exact same way as last year, the only difference is the CYA is lower at 30 compared to 60 and I have not added any calcium to bring the CH from 60 to the recommended level of 200-300ppm. I also haven't addded any borates to the pool and may not because I don't want to ruin a good thing!

I don't get it, the TA is the same at 90ppm as last year but my PH has been steady at 7.4 for almost a week now...it seemed I was always chasing the rising PH last year with acid additions every three days? I'm still adding about 500ml to 750ml of 10% chlorine daily to maintain 2-3ppm FC so that hasn't changed, same brand of bleach too (Chlorox).

Is the low CH the cause of this or maybe the borates? Because if it is it is awesome, I will never add calcium or borates to my pool again! Don't need it anyway, I only added calcium for the CSI balance which I assumed was necessary from a water quality standpoint. Water definetly feels softer too, both the kids and the wife have mentioned no more white flaky skin if they didn't shower after swimming.

Seems to be too good to be true?

 

[duraleigh]

Regardless of the reason for your lack of pH rise (it likely has nothing to do with your CH), there simply is NO requirement for CH in a vinyl lined pool anyway so CH of 60 is fine.

 

[chessie6]

Chuck, I find your post interesting because I'm having the same issue with my PH not rising either. I've been shocking for the past three weeks to get rid of pink algae and have added probably over 6 dozen bottles of bleach, yet my PH has held steady at 7.2 throughout the entire process. Last year, all I was doing was adding PH- nearly every day. Very interesting . .

Enjoy your pool!
Jan

 

[JasonLion]

Very likely it is the borates.

 

[RobbieH]

Yep, I bet it's the borates. Do you know what your borate level is? You will notice softer water, and more stable pH with borates around 30 to 50 ppm. Some, me included, use less chlorine also. It is one of the best things I've done to my pool.

 

[chem geek]

Just to be clear about this, 4JawChuck is saying that his pH is more stable with low CH and NO borates. He used borates in the past when the pH was rising more frequently. So in his case, if it's borates, then they caused the pH to rise more which is the opposite of what most people see.

I'm thinking that perhaps the older water had something in it that allowed for more rapid carbon dioxide outgassing though I don't know what that would be. His CYA was higher at the same TA level last year which means the carbonate alkalinity was about 10 ppm lower. So this is a bit of a mystery as to why the pH is stable now. Though we know about the affect of TA on carbon dioxide outgassing, maybe there are some effects from CH, borates, or CYA which are the three levels that changed. More likely, its something else we haven't identified.

 

[JamesW]

If the water is cooler than before, that would cause less carbon dioxide off gassing and less pH rise. If the old liner had a leak and there was a lot of water replacement, then that would affect the chemistry. If there is less aeration, such as from less usage, then there would be less pH rise.

 

[4JawChuck]

Hopefully we can find out the source of this mystery, I have been testing everyday and I am simply amazed.

Last year when we purchased the house the CYA level was through the roof, at the time I estimated 200+ but looking back at the water usage when I changed the water I am guessing it was closer to 400+. My water bill covered three 55 000 litre refills while I drained and added to get the CYA level down to 60ppm...crazy. I only drained a third at a time to keep from floating the liner, I was being careful.

When we removed the old liner there were no leaks from the 20 year old bleached liner amazingly, even the pool guys said I dodged a bullet...the sand/cement bottom was in excellent shape and there was no corrosion on the steel side panels. I did have the bottom resurfaced mainly to give radiused edges to the corners, the original pool install had sharp small radius corners and replacing the liner was a good time to do it...makes the vacuum work a lot better with smooth large radiuses. We found one return with slight cracking around the threads, no leaks from a pressure test but I said replace it anyway...I'm not taking chances.

A pressure test of the entire system showed no leaks except on the stair returns which had been plugged previously, I took the opportunity to cover those returns off with stainless steel plates and eliminate the bottom drain from the deep end as there was signs of cracking around the flange where the cover plate bolts go in. In my area bottom drains are notorious for freezing and bursting under ground...-40C will get em eventually. Usually what happens is the skimmer gets broken from being pushed out of the ground from frost pushing the line up from the bottom drain...seen a few nightmare scenarios from other pool owners and what can happen.

Needless to say I am convinced I was not losing water through the pool and saw no signs of it when we cut into the deck to replace fittings etc. I did the bucket test last year and it was exactly the same water loss as the pool.

Of course I didn't know vinyl liner pools didn't require calcium when we first moved in, I bought myself a CK2005 kit and read the Taylor manual to educate myself...actually it led me to this forum because I wanted to know more about manual dosing using regular bleach. Prior to getting here I went on a mission to get the CSI balanced and added calcium to get to zero CSI once I got the CYA under control.

Obviously there is something I don't understand about this chemistry because the PH hasn't budged in a week now, I've added about 4 litres of bleach over that time and seen the typical PH rise from the addition but it doesn't climb slowly. Last year I was adding bleach and acid on a regular basis just to keep it balanced. I checked my logs from last year once the pool was balanced and I estimate I was using about 500ml to 750ml of acid a week. It got to a point where I knew how much MA to add every week depending on how much bleach I was using...I wrote it down as a formula!

This year nothing, temps the same. FC is lower for the new low CYA level and CH is low at 60 but my TA is identical at 90...same as last year. I haven't added borates yet and likely won't because I don't want to mess with a good thing. The only other chemical in the pool was 2 litres of floc and 2 litres of sequester to get the brown out, I am pretty sure all the floc is gone from the last backflush...the water was brown as tree bark coming out of the filter and the pool is crystal clear. I have to say, I'm liking this stable PH thing...sure makes my life easier!

I'm wondering if a zero CSI isn't like trying to stand on a ball and +PH is the floor, trying to maintain the balance is tricky and falling off is easy with rising PH being what happens when you fall off. My CSI index is around -.62 by my color wheel, of course it tells me this level is "corrosive to concrete and metals" so it has me concerned but not overly so...my SS ladders and fittings look OK but who knows what the long term effects are.

If the worst thing that happens is my heater lasts one less year...I'm staying with it! Slugging MA into the pool can't be any better for it...right?

 

[dmanb2b]

What is the TA of your fill water?

 

[JasonLion]

When did you add the sequestrant? Sequestrant is acidic.

 

[4JawChuck]

TA of the fill water was 60, I used sodium bicarbonate to get to 90 according to the formula for 55000L which put it bang on to 90 so I know my volume calcs are good.

PH was 8.2 when the truck started filling, and it required around 3 litres of MA to bring it back down (after the sodium bicarb) to 7.5 after all was said and done.

I added 2 litres of sequestor (GLB Sequa Sol) on the second day after the fill was completed (which brought me to 7.4 PH), I added 2 litres of floc while the pool was filling since it was brown coming out of the truck...a lot of fine grey/black particulates precipitated from the floc during the fill...perfect time to add it when there isn't anything in the water yet. It took another day of recirc to clear the water, its crystal clear now but it plugged my filter quickly requiring a backflush on the third day. Definetly the sequestor was required because the pool immediately started clearing on application, pretty impressive to watch actually.

Checked again today and the PH was about 7.45-7.5 at an FC of 2ppm, hardly a rise compared to last year. We have been swimming every second day with 5-7 swimmers so I have been addding a lot of bleach to keep the FC up (probably 8-10 litres of 10%), cool windy weather is bringing in a lot of dust and dirt and a 32C temp pool plus a lot of rain has been demanding on the FC. It stays covered whenever we aren't using it with a solar cover, the rain has added about 2 inches to the pool level...enough that it countered the backwash so I haven't had to add any potable water.

Wonder if the sequestor stabilizes the PH? 2 litres was a lot to add if you read the instructions on the bottle...the pool guy wanted me to add 4 litres but I added half of his recommendation after reading the label (below).

GLB Sequa Sol

Initial Treatment:

Add 16 oz. per 10,000 gallons of water of normal hardness and mineral content. If the water is extremely hard (over 200 ppm) or has high iron, copper, or manganese content (over 0.1 ppm) double the initial dosage. Use 32 oz. per 10,000 gallons of water.

Maintenance:

Add 4 oz. per 10,000 gallons of pool water weekly as part of your maintenance program.

*If surface is black plaster, add Sequa-Sol after pool is full.