Is pH of 8.0 always a problem?

[HouTex]

I've touched on this issue a few times, but I don't think I've ever had this specific question. Here's my issue.

I've had rising pH since my pool was built 19 months ago, although it's slowly getting better. I have a spill over spa (although the water doesn't have far to fall--the top of my spa is even with the normal water level), a SWG and an oversized pump. My pH tends to reach around the 8.0 range and seems to top off before it gets to 8.2. I don't believe I've ever had a dark purple test result to match the 8.2 color sample in my test kit. I just get various shades of dark red. I usually add enough MA to lower the pH to 7.2 or 7.5 and then it goes back up over 4-5 days.

I tested my water yesterday evening after several days without adding MA and the pH was dark red. I figured it was around 8.0 so I added 48 oz. of MA and after an hour retested and the pH was right at 7.2. Using the pool calculator to back into my pH before the addition my pre-MA addition pH was at 7.9. So my 8.0 estimate was fairly close.

The pool calculator said my CSI was -.59 with 80 degree water after the MA addition. Note that 80 degrees is very unusual for SE Texas this time of year. We've had several days of overcast/rain. My temp would normally be around 89 which would lower the CSI to -.51.

Here are my full test results:

FC 5.5
CC 0.0
pH 7.9 (after MA 7.2)
TA 60 (usually fluctuates between 60-80)
CH 550
CYA 70
Salt 3400
Bortes 50

Before the MA addition the pool calculator says my CSI was -.14 at 80 degrees (but it would have been -.06 at my normal 89 degrees). Even if my pH was 8.0 at my normal 89 temp the CSI would have been negative at -.04. So my question is whether I should care so much if my pH gets to 8.0 or even 8.1 so long as I keep my TA low giving me a near zero CSI? Oddly, plugging in 8.2 for pH at my levels shows a CSI of -.16. That doesn't seem right. In any event, should I be concerned with pH at near 8.0 levels so long as my CSI stays near zero?

 

[JasonLion]

There is nothing inherently wrong with a PH of around 8. The main issues are that it becomes difficult to notice when the PH goes up, as you are already near the upper limit of the test, and high PH increases the risk of calcium scaling. As long as you can remain confident that the PH isn't going up above the limit of the test and your CSI remains reasonable you should be fine.

 

[onBalance]

I agree with Jason. Since your TA is only 60-70 ppm, CYA is above 50 ppm, borate is 50 ppm, the pH does begin to level off around 8.0. Unless you add a lot of an alkaline product, like soda ash, or bleach, without watching the pH and compensating with some MA, the pH will stay there and not climb higher than probably 8.2. The chlorine is less active at the higher pH, but if you maintain a good high residual of chlorine, that should not be a problem. However, it appears you have a SWCG pool, and the pH can climb higher with that type of system. So you do need to keep a close eye on the pH. If you were using Trichlor tabs instead, then there is little chance that the pH would go higher and cause scaling.

I have maintained my own personal pool for 30 years with a pH of 7.8 to 8.2 without scaling or algae problems, as long as I keep the CSI in balance, and brush the plaster finish often, and keep the chlorine level at 4 ppm or above. But I generally use acidic type of sanitizers, although I did use bleach for a few years.

 

[duraleigh]

OMG, I am so opposed to the direction this thread is taking. We do NOT advocate the use of pH higher than 7.8

The VAST majority of people on this forum want to swim in their pools, not spend the afternoon calculating csi or taking into account the thousands of variables that under certain circumstances can result in operating outside the normal parameters we suggest. The whole idea of our suggestions on acceptable limits is for people to feel comfortable staying within those limits.
Moved to the Deep End. JasonLion

I am not a book burner but I am committed to keeping this forum aimed at the K.I.S.S. principle of pool management. That involves keeping pH between 7.2 - 7.8 and TA and CH in line and you will NEVER have to do any additional calculations or variables.

 

[HouTex]

Duraleigh, I was loving the way the thread was going!!!!!

Seriously, for me, it's way more trouble (and thus not trouble-free, which is the goal here) to try to keep pH under 7.8. If I can safely manage pH in the 7.8-8.2 range that's way more trouble free for my pool than to try and keep pH around 7.5-7.8.

 

[duraleigh]

Seriously, for me, it's way more trouble (and thus not trouble-free, which is the goal here) to try to keep pH under 7.8. If I can safely manage pH in the 7.8-8.2 range that's way more trouble free for my pool than to try and keep pH around 7.5-7.8.

I'm happier that the thread is in the deep end forum. The goal here is to teach people that by following a certain set of guidelines they will have great success with their pools. Teaching people the myriad exceptions to those guidelines is confusing and uniteresting to the vast majority of people on this forum.

Your pool water has one H and two O's just like mine and everyone else's. We are interested in establishing targets that are applicable to everyone.

If 8.0 is fine and 8.2 is fine for a pool, why not 8.4 or 8.6. Shoot skip the 8's and just make it 9.0!!

....pH of 8.2 works, I know that....so does pH of 6.8....so does Baquacil....so does copper.......BUT all with qualifiers that make them troublesome in most cases......that's why people come to this forum in the first place.

My point is the suggested guidelines here work for the vast,vast majority of people (they will work for you, too) We do not teach the complexities of alternatives because they are just that....complex.

EDIT: Should be two H's and one O, and I rest my case for the need for simplicity.

 

[chem geek]

The only real issue with a higher pH pool around 8.0 or so is the risk of metal staining. If you don't have any metals in the water, then there should be no problem. Ben wrote about operating high pH pools at PoolSolutions in the link Operating Swimming Pools at High pH -- How, and Why?. As Dave says, this isn't something to promote as standard practice due to the risks of metal staining and of getting scale (if one is unable to have a lower TA or CH).

 

[HouTex]

Seriously, for me, it's way more trouble (and thus not trouble-free, which is the goal here) to try to keep pH under 7.8. If I can safely manage pH in the 7.8-8.2 range that's way more trouble free for my pool than to try and keep pH around 7.5-7.8.

I'm happier that the thread is in the deep end forum. The goal here is to teach people that by following a certain set of guidelines they will have great success with their pools. Teaching people the myriad exceptions to those guidelines is confusing and uniteresting to the vast majority of people on this forum.

Your pool water has one H and two O's just like mine and everyone else's. We are interested in establishing targets that are applicable to everyone.

If 8.0 is fine and 8.2 is fine for a pool, why not 8.4 or 8.6. Shoot skip the 8's and just make it 9.0!!

....pH of 8.2 works, I know that....so does pH of 6.8....so does Baquacil....so does copper.......BUT all with qualifiers that make them troublesome in most cases......that's why people come to this forum in the first place.

My point is the suggested guidelines here work for the vast,vast majority of people (they will work for you, too) We do not teach the complexities of alternatives because they are just that....complex.

EDIT: Should be two H's and one O, and I rest my case for the need for simplicity.

Dave, thanks.

I get that the goal here is to appeal to the vast majority of pool owners. That's the way it should be. But my pool has not behaved the way most pools seem to behave. I have an oversized pump, a spill over spa, and a SWG. Many on this forum have said, repeatedly, that those things will cause my pH to steadily rise. They seem to be right--pH continues to rise well into the pool's second year.

For me and my pool, I would rather manage my CSI by letting pH rise to around 8.0 before adding MA. I keep a close eye on the CSI and I'm never far off of zero either way. Otherwise, I'm messing with the pool more often than I'd like--and that's not trouble free for me. If the CSI means anything then I should be ok. According to onBalance and others my strategy seems to be ok--as far as my pool goes. I don't think you are saying otherwise. But I think you are stressing that to keep it simple for the vast majority of pool owners they should stay within the general parameters suggested here. That's ok with me.

 

[onBalance]

Keeping things as simple as possible should always be the goal. To keep pool water clear, add chlorine and filter it. This forum does a good job keeping things simple. But there are different water parameters that are recommended based on the type of sanitizers used, tap water differences, whether the surface is plaster, vinyl, or fibreglass, and water temperatures, etc, as it should be.

To his credit, Dave did not burn this thread, and is allowing other opinions. I believe TFP rightly adopted a slightly lower TA when SWCG systems or bleach is used. And I think it has also correctly adopted a higher pH range (7.5 - 7.8) for particular pools systems. IMO, the old 50 year industry standard a pH of 7.2 is too low, too close to 6.8 which is corrosive to equipment and plaster. I also believe the maximum recommendation of 7.8 is too low. I do not recommend maintaining a pH higher than 8.2, as my experience has shown that scaling is far more likely when the pH goes above 8.4. There is scientific evidence that a pH of 6.8 and lower, a pH of 8.4 and higher is likely to be detrimental to pools.

As far as metal solubility and staining, yes, copper is less soluble as the pH rises. But in the presence of chlorine, a pH of 7.2 or 7.4 is more corrosive to copper piping (if present) than a pH of 8.0. That is one reason I prefer a higher pH and preventing copper from being dissolved from piping. Dissolved iron in pool water will be oxidized whenever chlorine is added, and I believe that a pH of 7.4 versus 8.0 will make little difference in preventing iron staining. If there is evidence to the contrary, please make it known.

I have been chemically maintaining pools for many years, and have learned that a pH of 8.2 is not inherently bad or detrimental. If the CSI is at -0.3 with a pH of 7.4, then a pH of 8.2 is at a +0.5. I have not had a general scaling problem maintaining within these water parameters.

HouTex is exactly right. His pool water will be much easier to maintain if the TA is 60 ppm and allows the pH to settle around 8.0.

 

[chem geek]

Dissolved iron in pool water will be oxidized whenever chlorine is added, and I believe that a pH of 7.4 versus 8.0 will make little difference in preventing iron staining. If there is evidence to the contrary, please make it known.

Copper and iron staining should both be pH dependent. Though chlorine oxidizes the iron from ferrous to ferric state regardless of pH, the staining itself is due to copper and iron hydroxides or oxide-hydroxides and these ARE pH dependent. The use of a reducing agent can bring the ferric iron back to ferrous which is more soluble (because it doesn't as readily form hydroxides or oxide-hydroxides) and can then be bound to metal sequestrants.

We have examples where people already have chlorine in the pool but then shock it and have iron precipitate turning the water brown. The iron was already in the ferric state since there was chlorine already in the pool, but adding more chlorinating liquid or bleach raises the pH and the iron then precipitates. Just raising the pH through other means should cause a similar result.

 

[onBalance]

Yes, I agree. But that raises other questions. I have shocked pool water with chlorine and precipitated iron out of solution many times, then filtered, and yet no staining occurred most times. Could a high pH actually help prevent iron from staining plaster, as oppose to a lower pH that facilitates metal adhering to a plaster surface? I have also found that removing iron stains is easier on a smooth plaster surface, but is very difficult to remove iron staining from an older worn (etch) plaster surface. The same applies to copper stains.

 

[chem geek]

Ben Powell has referred to the technique you describe by adding 20 Mule Team Borax to the skimmer to create high pH and precipitate metals. The problem with any pH raising technique is to try and precipitate the metal into something caught by the filter rather than staining on a plaster surface. I know there are people who have reported getting metal stains come back when the pH rises so the technique would be a tricky one to do.

 

[onBalance]

Perhaps my point is being missed. Dissolved or soluble iron, which usually exists as ferrous bicarbonate, can be easily oxidized and changed into insoluble ferric hydroxide by oxygen or chlorine, and as stated above, regardless of pH. Once iron has been oxidized into an insoluble state, it can be filtered out by a D.E. filter. I did not have to raise the pH (above 8.2) to filter out oxidized iron. I have also oxidized iron with acidic chlorine gas, which lowers the pH.

I question the above senario where iron was already oxidized by chlorine, and then shocking and raising the pH caused the iron to precipitate out. Perhaps, there was more iron to oxidize? One ppm of chlorine only oxidizes about 1.6 ppm of iron. And raising the pH isn't necessary to oxidize iron. Iron can be completely oxidized at a pH below 7.0.

But back to my original thinking. I believe dissolved copper can react with calcium carbonate (pool plaster) and become copper carbonate or cupric hydroxide. I wonder if keeping the pH higher can actually help prevent staining by precipitating and filtering out copper before it stains the plaster?

As has been stated before, metals are less soluble at higher pH's. But look at it this way, a higher pH keeps the ppm levels of metals lower by precipitating out them sooner. And again, I don't like lower pH readings due to the fact that copper (and iron) can be attacked and dissolved (corrosion) easier by a low pH. A thought has just occurred to me in regards to dissolved iron. Since chlorine oxidizes iron completely, doesn't that make the "pH solubility" issue for iron irrelevant?

 

[chem geek]

Changing ferrous iron to ferric ion is caused by oxidation and is largely independent of pH, but the formation of ferric ions combining with hydroxide to form hydroxides or oxide-hydroxides is very pH dependent because the concentration of hydroxide is pH dependent.

2Fe²⁺ + HOCl ---> 2Fe³⁺ + OH^- + Cl^-
Ferrous Ion + Hypochlorous Acid ---> Ferric Ion + Hydroxyl Ion + Chloride Ion
-or-
4Fe²⁺ + O₂ + 2H₂O ---> 4Fe³⁺ + 4OH^-
Ferrous Ion + Oxygen + Water ---> Ferric Ion + Hydroxyl Ion + Chloride Ion

Fe³⁺ + 3OH^- <--->>> Fe(OH)₃(s) (or sometimes written FeO(OH)•H₂O)
Ferric Ion + Hydroxyl Ion <--->>> Iron Hydroxide (Iron Oxide-Hydroxide)

It's a matter of degree (the above is an equilibrium, though iron oxide-hydroxide is rather insoluble). If there's a lot of iron, then even at lower pH some iron oxide-hydroxides may form, but not as much as at higher pH. It sounds like what you are describing are much larger amounts of iron -- I was talking more about smaller amounts where staining would just get started. So what you describe (at any reasonable pH) could oxidize iron to precipitate the bulk of it, but to get the last of it, raising the pH would help.

Anyway, I still think it comes down to whether one can control the precipitation to occur outside the plaster rather than on the plaster and I don't know enough about such mechanisms to comment intelligently about the best approach that might work. What Ben described raising pH before the filter would seemingly force more precipitation to occur earlier to catch the metal in the filter and by forming it lower the pH back down somewhat to not have it cause staining in the pool (and for the time to be relatively short for the pH to be high anyway -- just long enough to backwash/clean the filter thereby removing the metal).