Brown stains and dry acid

#1
I've noticed brown stains in the pool recently. I found this post (Brown stains not from iron) which recommends vitamin C tabs as one of the tests.

I assumed I need something acidic, so I use dry acid (the stuff I use to lower pH levels). Placed a bit in a sock and "painted" the pool wall, and the brown came off quite easily (only a tiny bit of pressure required)

Was it ok to use dry acid as a substitute for vitamin C tabs?

Could this be an iron stain? (they are all over the pool, bar a couple of spots).
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,350
Tucson, AZ
#2
Dry acid is mostly sodium bisulfate which can form very strongly acidic solutions. It will definitely remove metal stains but it can also be quite corrosive to plaster. Ascorbic acid, on the hand, is less acidic but very good at removing iron stains because it is also a chelating agent. AA is the preferred way to perform the test for metal stains as it is non-destructive to plaster.

That said, it sounds like you have metal stains and that an AA treatment will help.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
#3
Dry acid is mostly sodium bisulfate which can form very strongly acidic solutions. It will definitely remove metal stains but it can also be quite corrosive to plaster. Ascorbic acid, on the hand, is less acidic but very good at removing iron stains because it is also a chelating agent. AA is the preferred way to perform the test for metal stains as it is non-destructive to plaster.

That said, it sounds like you have metal stains and that an AA treatment will help.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
Thanks Joyful.

Note to self: don't use dry acid for testing like that again :) My pool in vinyl so I hope i'm ok! (only a small area tested anyway)