PH keeps dropping to 7.0

[anthony21078]

New liner went in 6 months ago along with new coping/pavers. Years ago (2019), I had iron staining problems but ascorbic acid treatments combined with sequestrants and keeping the ph on the lower side (7.2-7.4), solved the problem. Along with a low ph, alkalinity was kept in the 50-70 range to avoid the ph swings. Since 2019, this worked great and my water was always balanced and clear.

New liner AND heat pump goes in 6 months ago and I kept the same mentality of low alkalinity (60-80) with a ph of 7.4-7.6. Again, balanced and clear water for the past 6 months. At first, I didn't want to deal with a solar cover so I had no problem running the heat pump longer to offset the heat loss. I found a free reel and solar cover on facebook marketplace about a month ago and figured I would give it a try now that air temps have dropped.

Learning to manage the the changes in chlorine levels with the solar cover was tricky but eventually I grasped how to adjust the the timers for the stenner to accommodate the minimal loss of chlorine. However, the PH keeps dropping to 7 and possibly lower over the course of 2-4 days after being brought to 7.4 with heavy aeration which usually takes 2 days. This has been happening for about a month.

I keep reading that solar covers don't affect ph levels but in my case, I cant find any other reasons for the ph to keep dropping. Last week I raised the alkalinity from 60 to 80 to see if that helped but as of today (and the ph pic posted below) looks like its below 7. I'm thinking the lower end of the alkalinity scale is causing the ph to drift lower with the cover? I'm wondering if I should keep raising alkalinity until this stops?

Also, I'm closing the pool sometime this week. I'm sure the ph will drop over the winter while covered the same way its been happening with the solar cover. Several months of low ph cant be good for a liner.

Other notes, once the ph was starting to continuously drift to the low side all the time, I disconnected the heat pump plumbing to avoid potential problems. My taylor kit is new with 2025 expiration dates.

FC is high right now because I have plans to close this week. I raised to slam levels about 5 days ago and fc has been slowly drifting downward.

Current water
fc 9
cc 0
ph below 7
ta 80
ch 240
cya 30

 

[JoyfulNoise]

How do you chlorinate your pool?

I see you use a stenner to inject LC.

Covers keep CO2 from outgassing and so that can cause pH rise to all but stop. Chlorine oxidation reactions tend to be acidic in nature but that’s usually just offsets the rise in pH when adding liquid chlorine. Your fill water may be slightly acidic and any precipitation that fills the pool will generally lower pH.

You can try raising TA but, honestly, if you’re going to close the pool then it doesn’t really matter. Just close it and forget about it until the spring

 

[anthony21078]

I found the fill water to be at a pH of 7.0 and below. However, I have not added any water in the past month (or since adding the solar cover) and there hasn't been any rain in my area for roughly 3 weeks.

In years past when opening in the spring I feel my pH was always around 7.4 which is where it was upon closing for the winter. Since that was an old liner I didn't really care that much about pH levels. Having a new liner and reading the adverse effects of low PH has me a tad concerned but since I can't figure the problem out I have no choice but to close

 

[JoyfulNoise]

It’s rather odd to have a pH of 7.0 and a TA of 80ppm. At that TA level, the equilibrium pH of water is above 8.0 meaning that the pH of the water can rise up to that level all on its own.

Are you rinsing out the test vial and making sure it’s clean between uses? Some people have a tendency to do the tests and then just toss the resulting mixture on the lawn and put the vial away. The vial should always be rinsed and dried after use and then, when testing, the vial should be rinsed with test water several times before testing. This ensures that there isn’t any contaminants in the vial that could mess up the test.

Do you have sources of aeration in your pool? If not, I would leave the cover off for a few days and brush the pool vigorously. Then test the pH again.

 

[JamesW]

The pH will only go down with a strong or weak acid.

A weak acid will lower the pH and not the TA.

Weak acids are acids like carbonic acid (carbon dioxide) or cyanuric acid.

A strong acid will lower the pH and TA.

Strong acids are acids like hydrochloric acid and sulfuric acid.

A cover will prevent loss of carbon dioxide, but that can only reduce pH rise, it cannot cause pH drop.

The first step is to make sure that you don't have a testing error.

The second step is to determine if the pH drop is accompanied by a corresponding TA drop.

Trichlor tabs will lower the pH and TA.

Adding CYA will lower the pH but not the TA.

 

[anthony21078]

It’s rather odd to have a pH of 7.0 and a TA of 80ppm. At that TA level, the equilibrium pH of water is above 8.0 meaning that the pH of the water can rise up to that level all on its own.

Are you rinsing out the test vial and making sure it’s clean between uses? Some people have a tendency to do the tests and then just toss the resulting mixture on the lawn and put the vial away. The vial should always be rinsed and dried after use and then, when testing, the vial should be rinsed with test water several times before testing. This ensures that there isn’t any contaminants in the vial that could mess up the test.

Do you have sources of aeration in your pool? If not, I would leave the cover off for a few days and brush the pool vigorously. Then test the pH again.

I would love to caulk this up to user error but Ive been testing my water the same way for years. FC first, dump, rinse with pool water several times, fill, test PH, repeat for other tests, rinsed and air dried.

No aeration whatsoever. Return jets barely break the water surface. When I need to raise ph with aeration, Ill place a sump pump in the water and use the return hose to create heavy bubbles.

I recall reading a post on here that said something like...," too low of alkalinity will cause ph to drift lower, too high of alkalinity will cause ph to drift higher." Something like that, and, you should find a number that keeps it stable because "every pool is different."

Following that statement, I figured I would raise TA a bit. I added soda ash yesterday to bring the ph to 7.6 and TA to 90. Dealing with a crazy amount of leaves on the solar cover and I was going to close today. However, Ill wait a few days without removing the solar cover and no additional chemicals to see what happens to the PH

 

[anthony21078]

The pH will only go down with a strong or weak acid.

A weak acid will lower the pH and not the TA.

Weak acids are acids like carbonic acid (carbon dioxide) or cyanuric acid.

A strong acid will lower the pH and TA.

Strong acids are acids like hydrochloric acid and sulfuric acid.

A cover will prevent loss of carbon dioxide, but that can only reduce pH rise, it cannot cause pH drop.

The first step is to make sure that you don't have a testing error.

The second step is to determine if the pH drop is accompanied by a corresponding TA drop.

Trichlor tabs will lower the pH and TA.

Adding CYA will lower the pH but not the TA.

The only acid that goes in the pool is muriatic acid but I haven't used in any in months.

TA has not been dropping when the PH drops.

I dont use trichlor, only liquid bleach.

CYA has was last added 2 months ago

 

[JamesW]

TA has not been dropping when the PH drops.

The only thing that can cause that is a weak acid like carbonic acid (injecting carbon dioxide gas), boric acid or cyanuric acid.

 

[JamesW]

There are other reports of the same issue with no explanation.

Causes for ph dropping in manually chlorinated pool

There are a lot of posts about controlling rising ph but ph in my pool continually drops. I only use bleach which I understand is net neutral. I don't use pucks so can rule that out. Rain could be acidic but it drops even with no rain and besides I have a hard cover so no rain gets in anyway...

www.troublefreepool.com

Ammonia getting oxidized will lower the pH and TA.

With no TA loss, the pH drop points to a weak acid like carbonic acid.