pool calculator muriatic acid woes

[calisoldier83]

Hi,

I have a 450 gallon J-470 Jacuzzi. Every time I perform a refill, I constantly have to add muriatic acid for about 3-4 days straight to get TA and PH at target. 

I'm using 14.5% strength from Home Depot. I'm going from a pH of 8 to 7.5 so thepoolcalculator calls for about 3 TBSP by volume. That doesn't make a dent.

I added about 20-25 TBSP over the course of 4 days to get TA down perfectly to 50 ppm and pH at 7.4. It's a long process in my eyes and it doesn't reflect what pool calculator recommends. I added about 2 TBSP at a time.

I'm trying to shorten this interval next time to 1 or 2 days. Any help would be appreciated.

Thanks

[RDspaguy]

3 hours ago, calisoldier83 said:

down perfectly to 50 ppm and pH at 7.4

What makes you think that is perfect? It's definitely not what I shoot for.

@waterbear can clear this up for you, I'm sure. 

[calisoldier83]

17 hours ago, RDspaguy said:

What makes you think that is perfect? It's definitely not what I shoot for.

@waterbear can clear this up for you, I'm sure. 

This post wasn't very helpful. You should read Nitro's guides.

 

 

[waterbear]

The only way to speed up the process is to aerate after dropping the pH to 7.0 but not any lower. This post is a bit more complete than Nitro's write up. It can take a LOT of acid (and you are using half strength, standard pool acid is 31% or 20 baume)

Depending on your initial TA, which you did not post,  lowering it to 50 ppm can take time and a lot of acid. The fastest way to do it is to use an acid demand test to drop your pH to 7.0 and not any lower and then aerate to outgas CO2. The act of lowering the pH lowers TA (converts bicarbonate ions to carbonic acid). Aerating then raises pH by outgassing CO2 without raising TA. This post will explain the process:

https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

 

[RDspaguy]

On 11/5/2020 at 1:55 PM, calisoldier83 said:

This post wasn't very helpful. You should read Nitro's guides.

 

 

The purpose of that post was to get @waterbears attention, and it was quite helpful in that respect. 😉

[waterbear]

I have to agree with RDspaguy, I was here (and in a few other forums) when nitro was writing his guides and know where the info came from and what he based it one. While his guide is good it's really not universal, particularly with the lowering of the TA since that really depends on how high the initial TA is and how much water is in the spa. The link I posted is safer and is actually something I has written in a different forum where I was a moderator and nitro was a member but their emphasis was on pools and not spas. The information on CYA was mostly calculated by Chem Geek but based on the work of Ben Powell from The Pool Forum years before nitro ever wrote his guide.

 

On 11/4/2020 at 6:07 PM, calisoldier83 said:

have a 450 gallon J-470 Jacuzzi. Every time I perform a refill, I constantly have to add muriatic acid for about 3-4 days straight to get TA and PH at target. 

IT sometime takes this long depending on your initial TA

On 11/4/2020 at 6:07 PM, calisoldier83 said:

I'm using 14.5% strength from Home Depot. I'm going from a pH of 8 to 7.5 so thepoolcalculator calls for about 3 TBSP by volume. That doesn't make a dent.

First, you should be using an acid demand test (get a Taylor K 2006 test kit if you don't already have one, it had the necessary test) and be dropping your pH to 7.0 to 7.2. You cannot use a calculator to determine accurate pH drop because there are too many other factors that will influence the outcome. Direct quote from the Pool Calculator (which, btw, was originally created by JasonLion at TFP and is an excellent tool if used properly)"

"Results are approximate and can be off significantly for large pH changes"

On 11/4/2020 at 6:07 PM, calisoldier83 said:

added about 20-25 TBSP over the course of 4 days to get TA down perfectly to 50 ppm and pH at 7.4. It's a long process in my eyes and it doesn't reflect what pool calculator recommends. I added about 2 TBSP at a time.

IF you initial TA is high this is not unusual. Once again, you are misinterpreting what the pool calculator recommends and is capable of actually doing with any type of accuracy.

Direct quote from the Pool Calculator :

"To lower TA you reduce pH to 7.0-7.2 with acid and then aerate to increase pH."

This is what I explain in my howto that I linked above and again below:

.https://www.poolspaforum.com/forum/index.php?/topic/28846-lowering-total-alkalinity-howto/

On 11/4/2020 at 6:07 PM, calisoldier83 said:

I'm trying to shorten this interval next time to 1 or 2 days. Any help would be appreciated.

one word: aeration! (In addition to using an acid demand test to drop your pH to the lowest safe level. Dropping the pH is what actually lowers the TA, aeration raises pH without raising TA. )Drop the pH to 7.0 to 7.2, aerate until pH climbs backup to 7.8 -8.0, test TA (it might not move much at first but when it does start dropping it goes pretty fast), use acid demand test to drop pH again (the amount of acid you need each time to drop the pH WILL change as the TA drops), aerate, test TA, acid demand test to drop pH, aerate...repeat until TA is on target then do final pH adjustment to desired level (but I would not go lower that 7.6 to 7.8). You might also might consider adding 30-50 ppm borate at this time for better pH stability plus all the added benefits of borate in the water if you are not already doing so. IF you do add borate then keep your pH in the 7.7 -  7.8 range and don't lower it until it hits 8.0. Don't lower it below 7.6 when you lower it.

Some truths about pH and TA that most manufacturers don't really understand but are based on the actual chemistry of the water:

THE MAIN CAUSE OF pH RISE IN A POOL OR SPA IS OUTGASSING OF CO2.

THE HIGHER THE TA (CARBONATION IN THE WATER), THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WIL RISE.

THE HIGHER THE AERATION OF THE WATER (OZONE SYSTEMS, SALT WATER SANITIZER SYSTEMS, AIR INJECTORS,  AERATION FROM YOUR JETS, 24 HOUR CIRCULATION ON HIGH SPEED, ETC.) THE FASTER CO2 WILL OUTGAS AND THE FASTER THE pH WILL RISE.

THE LOWER YOU PLACE THE pH THE FASTER IT WILL RISE (YOU ARE CONVERTING MORE BICARBONATE IONS, WHICH IS WHAT TA IS,  INTO CARBONIC ACID, ESSENTIALLY CO2 DISSOLVED IN THE WATER. THE HIGHER THE CO2 IN THE WATER THE FASTER IT WILL OUTGAS TO ACHIEVE EQUALIBRIUM WITH THE ATMOSPHERE.)

Hope this is helpful.