white powder ??? plaster????

Rockcrawler

Well-known member
May 8, 2007
174
El Paso, Texas
#1
15,000 gal IG, water is crystal clear, pool is 2 years old, this morning when brushing my pool, I noticed that when I brushed there was a white powder that followed the brush, I don't think its algae because it is white, could it be the plaster????

here are my pool numbers

FC 6
CC 0
PH 7.6
TA 120
CH 500
CYA 60-70

My numbers have been consistant, besides the FC, for the past 2 months

I would not think that it is the plaster because my TA and PH are OK

any opinions????

Robert :?:
 

Rockcrawler

Well-known member
May 8, 2007
174
El Paso, Texas
#3
simple No, I use liquid bleach and liquid acid.

when I first seen the white powder I thought it was plaster, but for my plaster to be failing my numbers would have to be bad.

also when I got done brushing the whole pool it wasn't as clear at before I started

the white powder actually came off the sides of the pool but not on every brush stroke
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
#4
Robert,

Your calcium carbonate saturation index is a little on the high side at about +0.4, but usually we don't see scaling until higher than that. Perhaps if the pH went up briefly at times then it could have precipitated some calcium carbonate, but that usually forms on the surface "hard" and not as dust and you'd probably notice the pool being locally cloudy after chlorine addition which it doesn't sound like you saw.

You could lower your TA to 80 or even as low as low as 60 if you wanted to and would be in balance. If your pool tends to rise in pH, then that would reduce that tendency to rise. Your high CH allows you to do this (i.e. have a low TA), so you might as well take advantage of it. Does your pH rise a lot and is it annoying for you? You clearly don't have to do this if it's not a problem for you. If the pH does rise a lot, then do you have aeration features (waterfall, spillover, fountain, shower, etc.)? The process for lowering TA is as follows:

ACTIVITY .......... pH .... TA ... (The following assumes 6.8 is the lowest measurement on the pH test kit)
==================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
------------------------------------
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration ............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

==================
Net of Above ....... 0 ........ -

Aeration is done using waterfalls, fountains, showers, spillovers, splashing, pointing the returns upwards, using an air compressor with a nozzle that produces tiny bubbles and is put into the deep end, etc.

I calculate that with your starting numbers and your 15,000 gallon pool it will take 64 ounces (8 cups) of Muriatic Acid (31.45% HCl strength) to lower the pH to 7.0. Then it will take a lot of aeration and an additional addition, over time as the pH rises from 7.0 to 7.2, of 128 ounces (16 cups) of acid. After that your TA should be at 70 and you stop adding acid and just let the aeration make the pH rise to 7.5. You should, of course, actually measure the pH and TA and not just trust my numbers -- generally you add half the recommended amount and see where you are at.

If you set your target TA to be 70 ppm, then you can have a target pH of 7.5 and probably keep it there reasonably, or you can have a TA of 60 and a pH target of 7.6 to 7.7

Richard
 

Rockcrawler

Well-known member
May 8, 2007
174
El Paso, Texas
#5
Richard,

Thanks for the in depth reply and great answers, My PH does rise rather quickly, I have to add about 8-10 oz of Acid every other day, and according to my saturation index, because I keep my pool water at 90 degrees it says I should have my PH around 7.1 for my water to be balanced, my TA started at the beginning of the season around 140 so once I got it down to 100-120 I was thrilled, but now that you mentioned it I will go ahead and dump some acid in and start aereating (waterfall) and thanks Richard now I know why my PH is rising, also I just got my CYA under control as well, last year I was using pucks, but after reading the forum at the start of this year I have been using bleach and along with normal splash out and backwashing my CYA is coming down, do you recommend lowering my CYA???

thanks for break down on lowering the TA

great info Chem Geek :-D

Also, about the white powder, it has not appeared again ?????

the Calcium Hardness, I am hoping it will lower through backwashing and splash out like the CYA
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
#6
Yes, you will solve two problems at once through a partial drain/refill or more frequent backwashing. All chemicals will get lowered including CH, TA, and CYA at least assuming your fill water is lower in CH and TA than your pool water (it certainly is zero in CYA).