pH and C.S.I. - which is most important?

[Aquatica]

Hi Guys,

I have problems getting enough CH in some pools as its not sold anywhere on the island.

Most pools are ok as the fill water is usually very high in CH.

I have to ship in CH from the U.S. So what I have been doing in the meantime is keeping the pH higher like around 7.8

Is this ok to do. pH is stable and does not move much at all.

I'm trying to balance C.S.I. If the C.S.I. is good and balanced does it matter if pH is 7.8 or even 8.0?

Here is an example of a pool I do this with:

pool size: 8K gals

FC: 6 < I'm lowering this.
CC: 0
pH: 7.8
TA: 100
CH: 180
CYA: 60
SALT: 2,900
TEMP: 75F
SWG: 30%
C.S.I.: -0.17

Thanks for any help.

 

[bobodaclown]

Numbers all look good. CSI looks to be in range. How's the water look? Even your FC is ok. I think I've read it's not a bad idea to keep your FC at 10% of your CYA. Here's a link for a good chlorine level chart:
http://www.poolsolutions.com/gd/best-guess-swimming-pool-chlorine-chart.html

 

[Aquatica]

Numbers all look good. CSI looks to be in range. How's the water look? Even your FC is ok. I think I've read it's not a bad idea to keep your FC at 10% of your CYA. Here's a link for a good chlorine level chart:
http://www.poolsolutions.com/gd/best-guess-swimming-pool-chlorine-chart.html

Thanks. Water looks great.

I usually try for 5% of CYA as I'm running SWG's. 8% for regular tablet run pools. But good to know 10% is not too high.

 

[PoolGuyNJ]

What kind of pool? Liner, plaster or f/g shell?

Scott

 

[Aquatica]

What kind of pool? Liner, plaster or f/g shell?

Scott

Hi Scott its gunite with diamond brite finish. pic of it here:

 

[JasonLion]

To compensate for low CH you will need to keep either TA or PH higher than you otherwise would. The main issue with raising TA to compensate, which is essentially where you are now, is that the PH will be less stable than it could be if you had CH up where it should be. If you lower TA, which will help stabilize the PH, you will need to allow the PH to drift up just a little more than where you have it now, say to 8.0, which isn't really a problem as long as CH remains low.

 

[Aquatica]

To compensate for low CH you will need to keep either TA or PH higher than you otherwise would. The main issue with raising TA to compensate, which is essentially where you are now, is that the PH will be less stable than it could be if you had CH up where it should be. If you lower TA, which will help stabilize the PH, you will need to allow the PH to drift up just a little more than where you have it now, say to 8.0, which isn't really a problem as long as CH remains low.

Great thanks Jason. I wasn't sure if going high on pH was going to stain or something. But if the CSI is good and slightly in the -0. then no possibility of staining?

I have to retest the TA. It might be slightly lower now since pH doesn't move that much now. I bought 40 lbs of CH. Need to add 10 lbs to this pool.

 

[duraleigh]

Aquatica,

If you add 10 lbs of CH to the pool, your CH will around 300+ and there is now no reason for your pH to be high.

 

[JasonLion]

Normally staining is not a problem with a PH of 8.0. Still, the risk of staining does go up as the PH goes up. If you are already using sequestrant to avoid stains you may need to increase the amount of sequestrant you are using to compensate for the slightly higher PH.

I should add that more or less everything discussed so far is micro management, which is hardly every worth the trouble.

 

[Aquatica]

Thanks for the info guys. I got some CH coming so will be adding to pools to get CH up and so I can run pH lower. Was just using the higher pH as a stop gap until I could get CH in.

Balancing will be much easier once we get enough CH.

 

[chem geek]

But if the CSI is good and slightly in the -0. then no possibility of staining?

The CSI has nothing to do with metal staining. It only tells you if calcium carbonate is over-saturated so can precipitate or scale or if it is under-saturated so can dissolve from plaster and grout. It also doesn't tell you how fast. With reasonably well-made plaster, a somewhat negative saturation index isn't going to noticeably dissolve the plaster. Likewise, a somewhat positive saturation index isn't going to result in scaling. That's why we allow for a range. In practice, for scaling, we usually don't see it until the CSI is around +0.7 or +1.0 or higher in most pools. In spas, I've seen reports starting at around +0.3 mostly in the heater.

Of course, with newer plaster that is curing, the pH near the plaster surface is much higher than the bulk water and in saltwater chlorine generator cells the pH is much higher at the hydrogen gas generation plate so scaling in these areas can occur even though the CSI is zero or a little negative in the bulk pool water.

The only risk from the higher pH is that of metal staining -- the higher the pH, the higher the risk. However, the pH at which staining actually occurs will depend on the quantity of metal ions in the pool. If you have zero or very low metal content in the water, then a high pH is no problem.

 

[Aquatica]

But if the CSI is good and slightly in the -0. then no possibility of staining?

The CSI has nothing to do with metal staining. It only tells you if calcium carbonate is over-saturated so can precipitate or scale or if it is under-saturated so can dissolve from plaster and grout. It also doesn't tell you how fast. With reasonably well-made plaster, a somewhat negative saturation index isn't going to noticeably dissolve the plaster. Likewise, a somewhat positive saturation index isn't going to result in scaling. That's why we allow for a range. In practice, for scaling, we usually don't see it until the CSI is around +0.7 or +1.0 or higher in most pools. In spas, I've seen reports starting at around +0.3 mostly in the heater.

Of course, with newer plaster that is curing, the pH near the plaster surface is much higher than the bulk water and in saltwater chlorine generator cells the pH is much higher at the hydrogen gas generation plate so scaling in these areas can occur even though the CSI is zero or a little negative in the bulk pool water.

The only risk from the higher pH is that of metal staining -- the higher the pH, the higher the risk. However, the pH at which staining actually occurs will depend on the quantity of metal ions in the pool. If you have zero or very low metal content in the water, then a high pH is no problem.

Thanks Chem. The swg cells tend to scale easily as you say. I try to keep csi like around -0.2 to -0.1 this seems to keep the cells clean. The pools stays in balance once the pH is locked in the csi doesn't move much. I will definitely be keeping some CH on hand from now on. and I really need to order some test kits to test for metals.