Dichlor / Bleach PH and TA Balancing trouble

[DKMin]

Hi, I have a Softub 140 and follow the dichlor bleach method. A week ago I did a fresh fill to prepare through winter, my municipal water is really good. Got CH to 140 then started messing with PH and TA. My TA was 70 but PH was high, I aerated and it went above 8 so according to the method, I needed to decrease TA. I got some muriatic acid and used the pool calculator to start lowering. I kept aerating and checked every 30 min or so. Once I finally got PH a little more stable my TA was 40! What do you do when TA is low but PH was drifting still? I checked both today after letting it rest 24 hours and PH was 7.4 I added baking soda to get TA back up, have not checked PH drift again.

I don't really understand the aerating PH drift. Does it do it everytime you aerate or does it eventually stabilize? When you're done aerating does it go back down or stay high?

Thanks for the help!

 

[Arobbert]

A TA of 40 is not necessarily bad nor is a PH of 7.4. You may have overshot things a little. It's better to go slow at the end and spread things out over a couple of days. I would have let be and checked it again the next day. If the PH is still low I would add a small amount of Borax to bump up the PH which will also raise the AK a bit. Do this gradually until you get a bit above 7.4 and the PH is stable there. Don't worry about the AK at this point unless your PH gets high which isn't likely with an AK of 40.

 

[jza1736]

I found the TA is happy at 40-50 in my Spa. When I first got my spa I chased my tail trying to get TA to 80 and pH in range. There's no issue with keeping it lower.

 

[Certified106]

I found the TA is happy at 40-50 in my Spa. When I first got my spa I chased my tail trying to get TA to 80 and pH in range. There's no issue with keeping it lower.

+1! When my TA is between 40-50 my PH will stay almost rock solid steady!

 

[DKMin]

Thanks for the replies, I let it sit for a day and this is currently what I'm reading.

CH 140
PH 7.6
TA 60

I did not do any aerating

 

[jza1736]

Looks good.
If your PH goes up, reduce it with muriatic acid or dry acid. I test my TA once a month and I leave it alone over 40

 

[Arobbert]

Thanks for the replies, I let it sit for a day and this is currently what I'm reading.

CH 140
PH 7.6
TA 60

I did not do any aerating

Good for now. The PH will probably go up after aerating. If it does take it down to 7.4, aerate, wait about 12 hours and retest. Continue that process until the PH stabilizes around 7.5 to 7.6 plus or minus .1 PM. The PH will likley stabilize with an AK of around 40 to 50. This can vary.

Remember that if the PH gets below 7.4 aerating will probably bring it back up. When you're in the final stages of PH adjustment it's a good idea to aerate and wait 8 to 12 hours before adding anything to raise or lower PH or AK.

 

[DKMin]

Great, thanks
So a CSI of -.2 is ok?

Does PH always creep when aerating or does it eventually stop? I'll be honest, my last water fill I only checked PH when the water was new, not continually after aerating.

 

[jza1736]

Mine stays in range, maybe once every 2 months I might have to add a little dry acid

 

[wogster]

Where TA (Total Alkalinity) needs to be kept between 80 and 120, are total automation systems that use ORP to compute sanitizer level, as the ORP number can be affected by TA. Low TA means a higher ORP, and a high ORP, will show a high sanitizer level, which can result in a low sanitizer level, because it's not feeding. If your not using a total automation system, it does not need to be as high.

 

[Arobbert]

Great, thanks
So a CSI of -.2 is ok?
This should be okay for a non "plaster, tile, stone, and pebble pool"

Does PH always creep when aerating or does it eventually stop? I'll be honest, my last water fill I only checked PH when the water was new, not continually after aerating.

Once you get it stable it will almost completely stop. Adding Dichlor will lower PH and AK as will MPS so liquid chlorine is preferred. In the winter I have to top off my water weekly which raises PH and AK. I address this by adding to the top off water the amount of acid needed to lower the AK to the level I'm currently using in the spa. If my PH gets a little low I add straight water to raise it a little. I don't usually need to do anything else. Once I've got things dialed in I only test every 3 to 5 days unless I'm making a specific adjustment.

 

[JamesW]

Where TA (Total Alkalinity) needs to be kept between 80 and 120, are total automation systems that use ORP to compute sanitizer level, as the ORP number can be affected by TA. Low TA means a higher ORP, and a high ORP, will show a high sanitizer level, which can result in a low sanitizer level, because it's not feeding. If your not using a total automation system, it does not need to be as high.

TA doesn't have a significant effect on ORP.

pH and CYA both have an effect on ORP.

Lower pH will result in higher ORP. This effect is moderated by CYA.

CYA reduces ORP significantly. ORP becomes almost useless if the CYA is over about 30 ppm.

ORP works best with no or very low CYA.

 

[jseyfert3]

Great, thanks
So a CSI of -.2 is ok?

Does PH always creep when aerating or does it eventually stop? I'll be honest, my last water fill I only checked PH when the water was new, not continually after aerating.

A negative CSI is of no concern with a vinyl or fiberglass spa.

pH shouldn't creep once you get it stabilized, until you add fill water which raises the TA or you add TA another way.

 

[JamesW]

The problem with high TA is that some of the bicarbonate turns into carbon dioxide.

The carbon dioxide offgasses due to aeration. It's the same process as a beer or soda going flat from shaking or heat.

As carbon dioxide offgasses, more bicarbonate turns into carbon dioxide to maintain the equilibrium between the bicarbonate and carbon dioxide.

When bicarbonate turns into carbon dioxide, it causes the pH to rise.

The percentage of bicarbonate that turns into carbon dioxide is determined by the pH.

The higher the pH, the lower the percentage of bicarbonate that turns into carbon dioxide.

So, the best way to reduce the amount of carbon dioxide is to lower the TA and to raise the pH.

If the TA is low enough and the pH is high enough, the amount of carbon dioxide will be low enough to stop or greatly reduce any pH rise.

There is carbon dioxide in the air, which dissolves into the water.

If the amount of carbon dioxide being lost is equal to the amount of carbon dioxide being gained, there will be no pH change.

 

[DKMin]

The problem with high TA is that some of the bicarbonate turns into carbon dioxide.

The carbon dioxide offgasses due to aeration. It's the same process as a beer or soda going flat from shaking or heat.

As carbon dioxide offgasses, more bicarbonate turns into carbon dioxide to maintain the equilibrium between the bicarbonate and carbon dioxide.

When bicarbonate turns into carbon dioxide, it causes the pH to rise.

The percentage of bicarbonate that turns into carbon dioxide is determined by the pH.

The higher the pH, the lower the percentage of bicarbonate that turns into carbon dioxide.

So, the best way to reduce the amount of carbon dioxide is to lower the TA and to raise the pH.

If the TA is low enough and the pH is high enough, the amount of carbon dioxide will be low enough to stop or greatly reduce any pH rise.

There is carbon dioxide in the air, which dissolves into the water.

If the amount of carbon dioxide being lost is equal to the amount of carbon dioxide being gained, there will be no pH change.

Great explanation, thanks everyone!

Is there a way to tell if a hot tub is dangerous to get in? I plan on checking often but what if free chlorine goes to zero for a day? Can't you shock it to around 10ppm and it'll be ok again?

 

[Arobbert]

Great explanation, thanks everyone!

Is there a way to tell if a hot tub is dangerous to get in? I plan on checking often but what if free chlorine goes to zero for a day? Can't you shock it to around 10ppm and it'll be ok again?

You really want to avoid it. If it's been less than 12 hours, the water is clear and there's no odor you may be okay. If you start going through a lot of chlorine you'll know there is a problem. If your CC levels are above 2 it's an indication there is a problem and will need to shock/slam per the instructions here:
https://www.troublefreepool.com/content/125-slam-shock-level-and-maintain-shockingl

 

[DKMin]

So if your chlorine demand stays within reason then it is safe water pretty much? I've heard of airborn bacteria, scary. I shocked to 10ppm and it lasted 4 days (did not use the tub during that time though).

 

[Arobbert]

So if your chlorine demand stays within reason then it is safe water pretty much? I've heard of airborn bacteria, scary. I shocked to 10ppm and it lasted 4 days (did not use the tub during that time though).

It's probably okay. What are your CC levels?

 

[DKMin]

It's probably okay. What are your CC levels?

I am on a fresh fill, so far I have only put 20ppm dichlor.

 

[Arobbert]

I am on a fresh fill, so far I have only put 20ppm dichlor.

Avoid letting it fall to zero and you will be fine.