Conflicting test results and pool scaling.

Problems relating to pH and total alkalinity.
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Conflicting test results and pool scaling.

Postby usmcpaul » Tue 29 Jul, 2008 16:32

Well first of all, thanks for this site, I have really learned a lot about my pool.

I have a 1.5 year old, 30,000 gallon, gunite pool with an autopilot SWG, and I am getting some very conflicting test results, as well as, conflicting advice.

This year after I opened the pool, the bottom plaster seemed to look dingy, and scrubbing it had no effect. My steps actually have 'foot prints' in them. I then noticed that the plaster walls are rough to the touch and no longer smooth like last year.

I have heard every reason in the book for why this has happend. The reasons seem to vary from from "high ph" to "abnormally low meteor activity"(lol). :shock:

The other day I took a sample of my water to be tested to a local pool store and he gave me some results that totally conflict with the readings I have been taking, the #'s on the left are his and the ones on the right are mine. I am using a Taylor 2005 test kit I bought last year.

CYA 0/ 20
TC .5/ (?)
FC 0/ .5
PH 7.3/ 7.6
TA 65/100
Total Hardness 325/ 370 ( I checked calcium hardness )

Salt level is 3400 ppm

After he sold me some stuff like TA increaser (Baking soda), 3 lbs. of CYA and some pool shock, I added them and here are the new numbers. Again his and mine.

CYA 28/ 50
TC 2.5/ >3
FC 2.5/>3
PH 7.9/7.5
TA 101/170
TH 328/380

I bought an electronic PH tester from Hanna industries and calibrated it, and my electronic readings match my test kit readings. So I think his machine is wrong there.

However, I am very concerned with the difference in the TA readings, and is my Calcim too high?, could the scaling on the walls be calcium that has precipitated out? Is there any cure for my scaling problems?

My PH has always been high, It averaged about 7.7 last year and it always rises, (as do most SWG's from what I have read). Should I be keepng it lower.

Please give me advice and some numbers to shoot for, considering my type of pool. I live in Michigan if that makes a difference.

Even if I have to drain the pool to fix this, I will.

Thanks, Paul.


Postby usmcpaul » Tue 29 Jul, 2008 16:40

I forgot to mention, I had him test for iron and copper, both were 0, and I tried stuff called "Jacks Magic" test kit to try and get rid of the dingy look.

Nothing in that kit helped my staining problem.

Thanks, Paul.
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Postby muss08 » Tue 29 Jul, 2008 20:32

Most of your numbers are fine. A general rule of thumb- if you dont let your test reagents freeze during the winter and you follow the directions for testing exactly then ALWAYS trust your test over a pool store's. The taylor k 2005 is a very good test kit (although the 2006 is better with a more accurate chlorine test). The problem with pool stores dont always calibrate their machines properly and dont rinse their tubes after every test so you could be getting risidual from other people's pools contaminating your sample.
Your CYA should be 60-80ppm for a swg pool. You should add 2lbs of cya. Your TA is now high because of the pool store. Because the pH always rises with SWG pools it is smart to keep your TA below normal. Normal TA is 80-120ppm. I would recommend 60ppm. This will slow the pH rise. You need to lower your pH down to 7.0 with muriatic acid. Then let is rise on its own and add more acid to lower to 7.0. Every time you add the acid it will also lower the TA as well as the pH. Keep repeating this process until you get down to 60-70ppm TA. Your hardness is fine. Normal levels are 125-400ppm. Your best bet is to keep the pH low and scrub the calcium deposits with a steel brush. You can also (PUT RUBBER GLOVES ON) put some acid in a bucket and use a sponge to sponge the acid onto the calcium deposits and scrub with the steel brush. Be very careful doing this!
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Postby Guest » Tue 29 Jul, 2008 20:53

Thanks Muss,

Do you have any idea why the bottom looks dingy, and what can be done to clean it up? The dingy look at the bottom looks worse when it is cloudy out. When it is real sunny out it doesn't look nearly as bad.

Was it the high ph levels that caused this?

Heres a general question; For a pool of this size, about how much Muratic acid should I be going through a week? I am using about 1 Gallon per week.

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