No Drain Acid Wash

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wmwinn

wmwinn

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LifeTime Supporter
Jul 14, 2012
36
Albuquerque, NM
For the last few seasons, I've seen more and more evidence of pool bottom and wall scaling. The pool is 10 years old (24K gallon), and the water comes from a well (which is hard to begin with). It's getting so bad, that swimmers come out of the pool with their feet bleeding. Very rough indeed.

This year, I want to try the No Drain Acid Wash for the next 5-7 days. Here are my current water conditions:

Temp = 74
FC = 3
CC = 0
pH = 7.5
TA = 140
CH = 600 !!
CYA = 0 (automatic pool cover, very little sunlight exposure)

I plan to take the pH down to 6.0, and brush 4 times a day with nylon and steel brush. I do not have a heater, no metals in the plumbing - so I plan to keep the pump on the entire time. That way, I want to see the cloudiness dissipate and perform necessary backwashing while the process is going on. If I can keep the water fairly clear during this process - the advantage is to know when the scale is gone, and then bring the pH back up using baking soda.

Is there a way to measure pH below 6.8?

Am i missing anything? This forum has helped me out many times in the past, and I'm getting a lot of education from other pool owners at TFP.

thanks,
- Mark -
 
You can not measure the pH that low directly, but by using the base demand test, I think that would give you an idea of what your pH is. This demand test is not part of the TF-100, but is part of the K-2006. What kit do you have?
 
I have the TF-100, and a K-1004 - which I believe tests the acid demand... but not the base demand.

Any advice of whether to utilize baking soda vs. soda ash? I realize that soda ash will use fewer lbs, but are there other advantages to soda ash?

thanks,
- Mark -
 
I added another gallon of MA today, knocked the TA down to 50. First 24 hours showed some minimal improvement with scale. I'm going to be very patient and let it work for another 3 days. Pump has been of the entire time. Brushed 4 times today.

Sent from my Nexus 7 using Tapatalk
 
Added another gallon of MA (total of 5 gal so far), TA has reduced further to 30. Scale remains on bottom of pool. I've been using a nylon brush, but will start using a stainless steel brush next. Each day, the CH has increased. Day 1: 600, Day 2: 630, Day 3: 725. I hope that means the calcium scale is going back into solution.

With a super-low pH during the acid wash - Can I trust the CH test results?
 
jblizzle said:
You can not measure the pH that low directly, but by using the base demand test, I think that would give you an idea of what your pH is. This demand test is not part of the TF-100, but is part of the K-2006. What kit do you have?
Click to expand...

I'm interested in hearing how the base demand test can provide me with an estimate of pH. After the normal pH test, I add Taylor reagent R-0006 to the sample, and count how many drops until a target pH color is seen. How will #drops get converted to a current pH? Is there a table somewhere that converts #drops to pH?

thanks,
- Mark -
 
Well there is a table with the kit that tells you how much soda ash (or something) would be required. You could then try to user PoolMath to back out the pH. But in hindsight not sure how accurate this would be since the demand test makes an assumption about your TA which may not match what you have.
 

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After 3 Days of the "No Drain Acid Wash" experiment, here are my findings:

Day 0 - FC: 3, pH: 7.5, TA: 140, CH: 600, Temp:74
Added 3 gallons MA, pump OFF, cover open, brushed 4 times with nylon brush

Day 1 - FC: 1, pH: << 6.8, TA: 70, CH: 630, Temp: 68
Added 3 lbs granular CYA, 12 oz algaecide, 1 gallon MA, brushed 3 times with nylon brush

Day 2 - FC: 0, pH: << 6.8, TA: 40, CH: 725, Temp: 66
Added 1 gallon MA, brushed 3 times with nylon brush

Day 3 - FC: 0, pH << 6.8, TA: 30, CH: 750, Temp: 68, base demand test: 5 drops
Added 1 jug of bleach, 1 gallon MA, brushed 2 times with steel brush

Without knowing the pH level, I'm having trouble figuring out how acidic the water is. The scaling along the walls and floors of my white plaster pool have not shown much improvement. I have some optimism around the CH increasing with each day - I would expect that as the water absorbs more calcium with such a negative CSI.

The idea to measure the base demand test was interesting. It only took 5 drops to bring the pH color back to a 7.5 reading. I don't have access to the Taylor base demand table - but found one on the internet that shows only 2.5 lbs Soda Ash for 20K pool for a 4 drop base demand test. That doesn't seem like much to me.

Perhaps my pH is not low enough?

Anybody have ideas what to do next? I have maybe 2 more days with this experiment before the family revolts and will want to swim. Anybody with "No drain acid wash" experience out there?

thanks,
- Mark -
 
Thanks for all the help and ideas during this experiment. Here are my conclusions and thoughts:

My 10 yr old pool was in dire need of an acid wash. Rough "sandpaper-like" scaling on bottom and walls of the pool. I did NOT want to dump the water for a professional acid wash - we live in a desert! There was a 4-5 day span of cold weather this spring, where my family knew that swimming was out of the question. Perfect timing to try this experiment.

My target pH during this "no drain acid wash" was 6.0. I believe I hit that number and kept it there for 4 straight days. Each consecutive day, there was an increase in the CH number, proof that some calcium was going back into solution.

I expected "clouds of dust" making it difficult to see the bottom when the acid started softening the scale. That did not happen. Water stayed nice and clear the entire time. After LOTS of brushing, I learned that steel bristles make easier work than the nylon brush variety. Very minimal "clouding" during each brush stroke along the white plaster.

I was worried about the stainless steel trim rings around my pool lights. Didn't want them to corrode and lose their finish. They stayed shiny and good looking during this project.

Overall conclusion:
I could have added more acid from the very beginning (try to get pH to below 5) and the results may have been better. Perhaps I was too "risk adverse" my first time trying this. There was some removal of my scale, which is good - just not totally removed. With such an acidic pool after the experiment, I decided to add Borates this year, and brought the pH back up using only Borax (608 oz of 20 Mule Team). Before the "no drain acid wash" my TA was 140, and afterwards it's sitting at 70 - much better for a SWG pool.
 
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