Constantly High PH
by Ian Sim
I have a pool of approx 25,000 gallons that was re-plastered in late Nov 2011. Outside temp was in the 50 day time and mid 30's at night. It took 40 hours to refill the pool with water. In coming water PH is 7.2.
After filling and start up completed by pool company, I had a really hard time keeping the PH below 8.2. I added pH Down by the pounds. The PH would drop to 7.4 / 7.6 for a day of so then back up.
I called Plaster company back in Jan as I had granular build up that felt like sandpaper when rubbed. They said that this is what happens when you don't treat a pool for 6 to nine months. They where dumbfounded when I told them that they had just re-plastered two months ago.
They decided that the only way to get rid of the build up to to acid wash my two month old re-plastered pool. They acid washed the pool heavily to remove and completed start up themselves.
Since that date, early Feb 2012 I retained a pool maintenance company to document the pools treatment. They are out every Wed and check pool water and I also check it every week-end also.
Since the acid wash to date ( 4 month )the pool has used 16 gallons of Muratic acid to hold the pools pH level between 7.6 and 8.2. The pool company adds 1/4 to 1/2 gallon on wed and I have to add another 1/2 Gallon usually on Sundays to knock the PH back down. The numbers.
Chlorine good at 2 to 3
Calcium Hardness 225
Phosphates started at 100 Feb 2012, now up to 250.
pH today before adding 1/2 gallon of Muratic acid 8.2 with pool equipment running for min of 3 hours after adding, pH down to 7.8
Plaster company says they have no idea, but it can't be from the plaster job. Four different pool maintenance companies also have no idea what is causing the high pH. They all say it must be the plaster.
Help, don't know what to do.
Thanks for the question Ian and sorry to hear about your issue
This is an area of debate and one huge area that has alot of chemical equations. Your issue is the re-plastering and pool start-up.
For years the pool industry has used 3 kinds of start-ups for pools. They are:
- Acid start-up. Keep the pH at 4.5 and alkalinity at zero for three days
- pH neutral. 1 gallon of acid was added to an 8000 gallon pool and balanced out after 3 days
- Traditional. The pool water has a slightly increased alkaline condition for 3 - 4 days, then balanced.
Then came along a new, and I think better, way to balance the pool and help the plaster. It's called the "Bicarb" start-up.
The acid start-up is the worst and most detrimental method. The pH of muriatic acid is already 4.5 so you can see what it can do to a newly plasterd pool.
This kind of start-up does help the surface look good for a while,
but it will deteriorate and stain easier.
Without going into too much detail and repeating what I've learned about the bicarb method, you can go to this link to learn much more:
To fix the pH issue, you need to know which kind of start-up the pool company used.
In effect, the bicarb start-up method adds enough bicarb to the fill water before adding it to the pool so that the alkalinity and calcium hardness equals 500.
Bicarb startup essentially adds enough bicarbonate to the fill water before adding it to the pool so that the TA + CH is equal to 500.
The fill water now has a pH level of 8.3 but will increase when the water is added to the pool because of the curing of the plaster. It can be lowered using muriatic acid to around 7.6 - 7.8.
The first month your total alkalinity (TA) remains high and the pH is kept slightly below 8.2.
There's a calcium carbonate surface on the newly plastered surface. By keeping a neutral or slightly positive Saturation Index (SI), you'll prevent the calcium carbonate in the surface layer from dissolving.
Normal range for this is -0.5 to +0.5. The Saturation Index is how well the pool is balanced with the chemicals added. 0.0 is neutral. But even if you keep the SI positive, the pH will still increase.
What's happening now in your pool is the plaster is converting from calcium hydroxide into calcium carbonate. It's like layers of an onion. First layer is calcium carbonate and the 2nd is calcium hydroxide.
Here's something that you might be interested in. To my understanding the calcium carbonate forms on the surface. The underlying plaster areas remain calcium hydroxide as such because it's too deep for the water to penetrate, react, and convert the plaster into calcium carbonate.
But, if the newly formed calcium carbonate is somehow dissolved, as in the case of an acid wash, then it will expose the underlying calcium hydroxide layer, The hydroxide will be released, which will cause the pH to rise.
Like I said early on, this is a huge area with lots of chemical equations.
Take a look at the link above. That has so much information that it would be difficult to write about.
Find out the kind of start-up the pool company used and you can go from there. In my opinion, doing an acid wash on a newly plastered pool is wrong. It's like rubbing sand paper on a new born baby. The skin is delicate so don't do it.
My opinion is the start-up may not have been done properly, but again, without knowing the kind of start-up that was done, it's hard to say.
To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Start Up/Opening A Pool" category.
Check back to this post for updates or answers.
If you need immediate assistance (within 24 hrs) or for emergency personal assistance, you can make a donation of your choice and I'll answer your questions by phone.
Hope this helps and have a great Summer.