Plaster is like Sandpaper

[PoolDoc]

You need to maintain a chlorine level around 10% of your CYA (9 ppm), so your chlorine is way too low. You'll grow algae at your current level. But use bleach, not your SWCG to shock. Trying to 'boost' or 'shock' using an SWCG leads to greatly reduced cell life.

Your pH is too high; you need to keep it lower. But you may be dissolving pool plaster that's ALREADY softened and weakened. So, I wouldn't go too low. Maybe, 7.6 - 7.8.

BUT . . . you need to inspect your SWCG cell; the plates may need to be cleaned, given all the movement in pH, calcium and TA levels.

[Mikes Pool]

You need to maintain a chlorine level around 10% of your CYA (9 ppm), so your chlorine is way too low. You'll grow algae at your current level. But use bleach, not your SWCG to shock. Trying to 'boost' or 'shock' using an SWCG leads to greatly reduced cell life.

I've never used bleach, is there a formula for how much to use?

Your pH is too high; you need to keep it lower. But you may be dissolving pool plaster that's ALREADY softened and weakened. So, I wouldn't go too low. Maybe, 7.6 - 7.8.

Today, my pH is 7.4 after adding acid last night. My alkalinity went from 110 last night to 70 this morning. Is that because I turned the bubblers off? Am I at the point now where I can control my pH by bringing up the alkalinity?

BUT . . . you need to inspect your SWCG cell; the plates may need to be cleaned, given all the movement in pH, calcium and TA levels.

I will inspect the SWCG tomorrow.

[PoolDoc]

Your PF is 4.8. Walmart 8% bleach, per gallon, is equivalent to 0.7 lbs of chlorine gas. So 1 gallon will add 4.8 x 0.7 ppm chlorine to your pool, or 3.4 ppm.

Likewise, if you use dichlor (61% available chlorine in some forms), 1 pound would add 4.8 x 0.61 = 2.9 ppm.

I'm not sure why your pH is moving; there are multiple possibilities. Focus on managing your chlorine, keeping your pH between 7.0 and 7.8, cleaning your SWCG. Run things for a week or two so you establish 'normal' patterns.

[Mikes Pool]

I am posting my pool readings for the last 11 days. As you can see pH is all over the place. I pulled the SWG and it was pretty clean but I followed the mfg. instructions and acid cleaned it anyway.The water is very clear and I don't see any dust when I brush. Come to think of it, last year when I brushed I would always see dust. That must have been when my plaster was being attacked! Also, last year is when my original Jandy SWG needed replacing. During that time my pool chemistry got out of whack as the SWG quit right before our vacation and I neglected the pool for about a week. It's all starting to make sense now. I feel like I have things under control now but it is driving me nuts chasing the pH like that. Any suggestions on the pH? Am I resigned just adding acid every other day?

As for the chlorine, I read elsewhere on your site that 4.5% of CYA is good for a SWCG pool and you are saying 10%. Why the difference?

One more thing Doc. What are your thoughts on a "No drain acid wash"? My plaster is blotchy now and I was wondering if that would help with the blotchiness and maybe smooth the plaster at the same time.

Here are my pool readings:


Date FC/ CC/ pH/ TA/ CH/ CYA

7/13 1.0./ 0.0/ 7.8/ 110/ 320/ 90/ Added 3 pts. MA

7/14 2.5/ 0.0/ 7.4/ 70/ 300/ 80/

7/15 2.5/ 0.0/ 7.6/ 100/ 300/ 80/ Added 1 pt. MA

7/16 3.5/ 0.0/ 7.8/ 100/ 300/ 80/ Added 1 pt. MA

7/17 4.6/ 0.0/ 7.8/ 80/ 300/ 75/ Rain, no acid

7/18 5.4/ 0.0/ 8.0/ 100/ 300/ -- Added 1 pt. MA

7/19 5.0/ 0.0/ 8.0/ 75/ 300/ -- Added 2 pts.MA

7/20 6.8/ 0.0/ 7.6/ 75/ 300/ --

7/22 6.5/ 0.0/ 8.0/ 100/ 275/ 80/ Added 1 pt. MA

7/23 5.8/ 0.0/ 7.8/ 75/ 275/ --

7/24 6.4/ 0.2/ 7.8/ 75/ 275/ -- Added 1 pt. MA

[Mikes Pool]

I wasn't sure if I should make this a new question so I'll just stay on this thread.
I have been monitoring my pool chemistry almost every day since July 13 2014. Since that time I have added 12 lbs. of baking soda and 6.25 gal. of Muriatic Acid. All of my numbers are good:

FC 6.8
CC 0.0
pH 7.8
TA 90
CH 275
CYA 70

My question has to do with my pH. It is always high. As you can see I am continually adding acid. It just seems like a lot of acid. I am wondering if my pH is just normally high and if there is any thing to worry about with a high pH. My K2006 test kit only goes up to 8 so I am not sure how high my pH actually goes. Is there a different test kit that has a higher pH range? How high is too high? Do some pools naturally have a high pH? This is driving me nuts! Any advice is greatly appreciated. Thank you.

[chem geek]

You've been adding too much baking soda. Have your TA be lower at 70 ppm. Also consider using 50 ppm Borates. Only add acid to get to around 7.5 pH (not below) and let the pH get to 7.8 or so before adding acid. Also, if you have a short pipe run between your SWCG and the pool, point that return more downwards to help dissolve chlorine gas bubbles because if they outgas that will have the pH rise. The hydrogen gas bubbles from the SWCG also aerate the water which increases carbon dioxide outgassing that raises the pH. Having a lower TA target and higher pH target helps reduce that problem.

[Mikes Pool]

Quote Originally Posted by chem geek

You've been adding too much baking soda. Have your TA be lower at 70 ppm.

*My TA was around 60 so that is why I added baking soda. Low TA and aeration is what caused erosion of my plaster so I am worried about that and was shooting for a mid-range level.

Also consider using 50 ppm Borates.

*What are the Borates for, to lower my TA?

Only add acid to get to around 7.5 pH (not below) and let the pH get to 7.8 or so before adding acid.

*My pH generally goes from 7.6 to 8.0 overnight.

Also, if you have a short pipe run between your SWCG and the pool, point that return more downwards to help dissolve chlorine gas bubbles because if they outgas that will have the pH rise. The hydrogen gas bubbles from the SWCG also aerate the water which increases carbon dioxide outgassing that raises the pH. Having a lower TA target and higher pH target helps reduce that problem.

*I do have short pipe runs. The returns are aimed so that it barely ripples the surface of the water. What is the correct way to aim the returns? Should I aim all 5 of them down?

Thank you again for your time and expertise.

p.s. I apologize for the structure of this reply. I haven't figured out the tools.

.

[chem geek]

My TA was around 60 so that is why I added baking soda. Low TA and aeration is what caused erosion of my plaster so I am worried about that and was shooting for a mid-range level.

It is not just low TA and aeration that can dissolve plaster, but also low Calcium Hardness (CH) and low pH. It is the combination that you want to saturate the water with calcium carbonate. So you can readily have a lower TA level of 60 or 70 ppm if you don't lower the pH as much and you raise your CH level. A higher TA will have the pH tend to rise faster. I'd shoot for 70 ppm and raise your CH as needed. Let's say you plan to keep your pH in the 7.6 to 7.8 range and that you have your CYA level at 80 ppm (to minimize chlorine loss so you can turn down your SWG on-time) and have a minimum FC target of 4 ppm. Assuming 3000 ppm salt, you could raise your CH to 500 ppm to have a saturation index of -0.2 at pH 7.6 and 0.0 at pH 7.8 which should be fine (you could have your CH at 400 ppm and probably be OK since your pH tends to stay towards the higher side).

What are the Borates for, to lower my TA?

The 50 ppm Borates are for additional pH buffering that should slow down the rate of pH rise and also prevent scaling in the SWG cell.

My pH generally goes from 7.6 to 8.0 overnight.

This is probably a combination of your TA being too high and having the short pipe runs not fully dissolving chlorine gas. The use of 50 ppm Borates will also slow down this rise though won't change the amount of acid you need to add. Having your CYA level at 80 ppm will help because it will protect chlorine from sunlight more even with the FC higher to maintain a 5% FC/CYA ratio (i.e. 4 ppm FC with 80 ppm CYA). Losing less chlorine to sunlight means you should be able to lower your SWG on-time and that will reduce the rate of pH rise since there will be less aeration of the water from the hydrogen gas bubbles and less chlorine gas that escapes.

I do have short pipe runs. The returns are aimed so that it barely ripples the surface of the water. What is the correct way to aim the returns? Should I aim all 5 of them down?

I would point the returns that are closest to the pump downwards or diagonally downwards (depending on the type of flow you want). You'll probably need to keep some returns pointed so that you get some surface water motion to be able to move debris to the skimmer.

[Mikes Pool]

Thank you Chem Geek. I think you have illustrated how each pool (mine, for example)is different and how the pool store's cookie-cutter approach doesn't work for all pools.

I have followed your advice up to this point;

The TA mysteriously went down to 70. This is after adding baking soda 2 weeks ago to bring it up to 90. I'm glad that it went down on it's own as I understand the process in attempting to lower it. I just hope it doesn't keep dropping.

I increased the CH to 425 from 275.

I adjusted a few of my jets and changed the pump run-time from 14 hours a day to 9 hours a day. I also increased the chlorine output on my SWCG to compensate for the reduced run time. Will this cause an increase in gas bubbles?

Today the pH was 7.8 and the FC was 5.4. CC was 0.0 My CYA is still at 70 but I will bring that up.

The one thing I'm not sure of is the Borates. What is it and with what do you increase it and measure it?

I want to thank you again for taking the time to help me with this and to be a more educated and trouble free pool owner.

[CarlD]

I can answer that last one:
You add borates by adding ordinary 20 Mule Team Borax, which we also recommend first for increasing pH (so you have to add acid to control pH).
There are borate test strips which are about the only test strips we recommend. Higher borates inhibit algae and make the water feel softer.