How much muriatic is reasonable?

[Drew80]

The pH is always creeping up in my pool - I add a little under a cup of muriatic per day, on average. I initially chalked it up to the pool being new (2018) but it seems like this shouldn't still be an issue. I've had pools before and never had pH issues, but they were all older. Is this normal for a two year old pool?

Before adding acid this morning:
pH - 8.2+
TA - 90
FC - 4
CH - 150
CYA - 70
Salt - 3000

 

[DiverGirl1972]

I'd imagine every pool is a little different depending on the type, age, equipment used (swg) and fill water chemistry. I'll be no help to you, but in three years, I've never had to reduce my pH. I actually bought a couple of gallons of muriatic acid when I first switched to TPF, thinking that I would eventually need it, but nope! They still sit in the corner of the garage just taking up space.

Do you know the pH of your fill water?

 

[lager1829]

I looked at Pool Math effects of adding - for your size pool, I'm seeing a drop of only .2 pH adding 8 oz of 31% MA. Do you test about an hour after adding? Try getting it down to 7.6 then it might settle in at 7.8 as salt water pools tend to do.

 

[Drew80]

I'm in the habit of measuring every day or two right now. When it's 8.2+ as it was this morning, I add two cups of muriatic, which should bring it down to 7.4-7.5 according to poolcalculator. Sometimes it will be lower and I'll add less.

I just added acid about 30 minutes ago. I'll measure again in a bit.

 

[poolnoobgrandma]

Our pool just turned one, and the acid demand is finally slowing down. I'm down to adding about 20 ounces every week or so. That's way down from where it was even last winter.

 

[JJ_Tex]

Most pools rise in pH, but you can help slow down that rise by:

1. Limiting the aeration. I see you have a spillover spa. How long is that running each day? Try limiting that and any bubblers, etc that aerate the water.
2. You can try lowering your TA a bit as 90 is the upper limit of TA and is causing your pH to rise.

 

[Holydoc]

I agree with JJ_Tex. I would keep lowering my pH to 7.2 to bring the TA slowly down. The lower your TA, the less tendency for the pH to rise. Currently the high TA, is contributing to your pH rise. Lower the TA down and see if that slows your pH rise.

 

[Drew80]

Most pools rise in pH, but you can help slow down that rise by:

1. Limiting the aeration. I see you have a spillover spa. How long is that running each day? Try limiting that and any bubblers, etc that aerate the water.
2. You can try lowering your TA a bit as 90 is the upper limit of TA and is causing your pH to rise.

1. My pump runs for 6 hours a day, currently. The spa level is even with the pool, so the spillover drop is only the difference in water level which is less than an inch. Also my return for the cleaning cycle is about 80% pool / 20% spillover, so it's really just a trickle. Aeration should be minimal.
2. I understand that TA causes pH to buffer, but I have to add acid to lower my TA too and it doesn't stay put either. After a few weeks, my TA is right back up. At times, I've been in the 300s on TA, so 90 is actually low for me. I've also gotten conflicting advice on TA - some people tell me to ignore it and only watch pH. So IDK.

 

[Edc1911]

I add 3 cups every 3 days.

 

[tillmac62]

What is the TA of your fill water? If it's high enough, it will offset the TA reduction caused by your acid additions - which would explain why your TA is higher after "a few weeks" later.

 

[Palpatine]

My plaster is less than a year old, I've been running my pump a lot lately, like 18 plus hours a day but my TA is only 30... I seem to go through about a gallon of MA every week or two. Seems high to me also.

 

[Drew80]

What is the TA of your fill water? If it's high enough, it will offset the TA reduction caused by your acid additions - which would explain why your TA is higher after "a few weeks" later.

60-ish

 

[tillmac62]

60-ish

If 60 is correct, how did it get to 300 several times? For your fill water, 300 is the equivalent of letting your pool evaporate 5 times...

 

[Drew80]

If 60 is correct, how did it get to 300 several times? For your fill water, 300 is the equivalent of letting your pool evaporate 5 times...

The 60 number was just now, so it's correct as of today. Maybe TA fluctuates in municipal water? I seem to remember measuring TA when I initially filled it two years ago and found it to be much higher, but I didn't write it down.

Edit: I just looked back at my previous posts. Apparently I measured tap water TA at 350 back in 2018, so Austin's water has changed.

 

[tillmac62]

The 60 number was just now, so it's correct as of today. Maybe TA fluctuates in municipal water? I seem to remember measuring TA when I initially filled it two years ago and found it to be much higher, but I didn't write it down.

Edit: I just looked back at my previous posts. Apparently I measured tap water TA at 350 back in 2018, so Austin's water has changed.

That makes sense to explain the 300 result. If your fill water is 300 now, 90 would be almost impossible to obtain. pH is what you want to control. Minimize aeration and lower the pH when it hits 8. Lower to the low to mid 7s using MA. With 60 TA fill water, you'll eventually get the TA down a bit. Take advantage of rain by lowering your pool a bit before a storm. Don't chase the TA level. Just don't let it drop below 50 because the purpose of TA is to buffer a potential drop in pH.

 

[Drew80]

Just don't let it drop below 50 because the purpose of TA is to buffer a potential drop in pH.

A drop from what? I've literally never had a pH drop that I didn't cause.

 

[tillmac62]

It's to protect equipment from acidic conditions. Accidents happen...a kid pours a couple of gallons of MA in instead of liquid chlorine. In my case, my fill water has a pH of 7.1. I actually have to raise my pH.

 

[Drew80]

It's to protect equipment from acidic conditions. Accidents happen...a kid pours a couple of gallons of MA in instead of liquid chlorine. In my case, my fill water has a pH of 7.1. I actually have to raise my pH.

Ah, I see

 

[Drew80]

I just tested after adding muriatic and running the pump for a few hours

ph - 7.5
TA - 80

Should I add more acid to bring these down more?

 

[tillmac62]

You can, if you wish. I wouldn't do anything else until it reached 7.8 - 8, then drop it to 7.5 or a bit less. Lower TA levels will slow the pH rise but not eliminate it. Minimize aeration - that is what really drives pH rise because of CO2 outgassing.