Scale Formation and Chemistry

[benavidescj]

Happy Holidays everyone!

I was curious, I always hear that you should keep your Ph lower than 7.8 to avoid scale. Is this just a rule of thumb, or can the pH get higher depending on the chemistry of the water? Is it more dependant on the CSI value? In my case I have a high CH and low temperature. Right now my pH is at 7.95 and I am thinking of leaving it there because my CSI value is -0.25.

Test Values:
pH: 7.95
CH: 520
TA: 70
CYA: 60
FC: 5.5
Salt: 4000
Borate: 50
Temp: 47
CSI: -0.25

 

[257WbyMag]

You are correct in that your CH being high and your temp being low, you can get away with a higher pH to compensate. As soon as that water temp comes up though, things are gonna be off the chart. You should probably look at bringing down the CH at some point.

 

[iPhone]

I personally don't like high pH especially when pushing 8.0 as you are, no matter what the other tests read. Its bad for pool and equipment.

If it were my pool, I would knock it back down to 7.4. Chlorine works better at that pH and with the correct amount of TA (depending on the type pool you have) the pH should stop bouncing and stay in the 7.4 to 7.6 range. Total Alkalinity is your pH buffer to prevent bouncing.

Remember to read pH at pool water temperature and all the other readings need to be tested at room temperature.

 

[chem geek]

The possibility of scale is based on the CSI, not the pH alone. However, if there are metal ions in the water, then high pH can cause staining to occur even if the CSI is otherwise low. This is because the staining can come from metal oxide-hydroxides that occur at higher pH, even if the CH and TA are low. As for chlorine effectiveness, with CYA in the water to buffer hypochlorous acid (as shown here) the reduction in active chlorine level with higher pH going from 7.5 to 8.0 is only a drop of 14% which one can easily make up with a slightly higher FC target.

If you don't have metal ions in the water and your CSI is low, then one can operate their pool at a higher pH, but it's tricky. More detail about operating a high pH pool is in this article at PoolSolutions. This is not a normal situation or recommendation, but it can be done.

Also note that the pH naturally rises when water gets colder and this helps keep the CSI from dropping as much.

 

[benavidescj]

I personally don't like high pH especially when pushing 8.0 as you are, no matter what the other tests read. Its bad for pool and equipment.

Can you be a little more specific on what bad things this does to pool and equipment?

 

[benavidescj]

I guess I should have also stated that this is only temporary for a couple, three months during the winter. My plan is to lower the CH and pH in the spring.

 

[chem geek]

So long as you don't have metal ions in the water, I don't see a problem with you running at a higher pH over the winter. Some municipal water suppliers deliver water in the 7.8 to 8.2 pH range.

 

[benavidescj]

So long as you don't have metal ions in the water, I don't see a problem with you running at a higher pH over the winter. Some municipal water suppliers deliver water in the 7.8 to 8.2 pH range.

If I want to check for metal ion, which one's should I check for? Copper comes to mind. Is there a kit you recommend or is it multiple kits?

 

[chem geek]

The kits aren't cheap (Taylor K-1264 is $91.60) -- copper and iron would be the most common metals. Copper would generally only come from a copper-based algicide, though could come from copper piping if it got corroded, say from very low pH. Iron can come from cheap stainless steel or other iron exposed to pool water (especially at low pH). You could have it tested at a pool store.

You could take a white bucket of pool water, add 20 Mule Team Borax to it to raise the pH to a high level, and see if you notice green (copper) or yellow/orange (iron) color or precipitate. Adding one teaspoon to 2 gallons of water would raise the pH to around 9.0 (with Borax, you can't raise the pH above 9.1). You might get some white calcium carbonate, but that's OK.

 

[iPhone]

I personally don't like high pH especially when pushing 8.0 as you are, no matter what the other tests read. Its bad for pool and equipment.

Can you be a little more specific on what bad things this does to pool and equipment?

It can cause scaling or calcium buildup on pool surfaces, waterline and accessories. Water becomes dull or cloudy and clogging of filter medium or elements can happen. Other parts of your pools water content can reduce or lower the effects of high pH, but why chance it? Currently you are probably OK, but all it takes is for one component to change and issues can start.

I just don't like bouncing pH or pool water that is out of balance. To me its just easier to keep stuff where it is supposed to be, but I keep both of my pools open year round.

 

[benavidescj]

If you don't have metal ions in the water and your CSI is low, then one can operate their pool at a higher pH, but it's tricky. More detail about operating a high pH pool is in this article at PoolSolutions. This is not a normal situation or recommendation, but it can be done.

Richard,
When you say this is not "a normal situation or recommendation", are you saying this purely from a metals stand point or are there various other reasons? I just don't want to change things if they are stable and frankly better (CSI) in my particular situation. I keep hearing my CH and pH are high but the calculator says I am not (again CSI).

 

[chem geek]

If you don't notice any metal staining, then leave things as they are and just make sure the pH doesn't go higher than the next to highest level on your test kit and that the CSI doesn't get very high (unlikely in your situation).

In my own pool, I can notice some iron metal stains in one part of the deep end (a yellowish broad cast, actually) faintly returning when the pH gets to 7.8 or so as the water gets cold. I continue to have remnants of a rust problem from stainless steel mounts where the Trichlor feeder got too close 7-8 years ago. I am not lowering the pH and will deal with this on spring opening, probably doing another ascorbic acid treatment and maybe trying out CuLator to see if I can actually remove the metal ions (though I'll need to get someone to fix the darn rusting or else the problem will keep reoccurring).