Cause and remedy for the wall stain

[Eric_yang]

Hi just wonder how can I treat the pool wall stain, as shown in the attached picture. The stain cannot be brushed off. I have been running the cleaning robot 30min daily and brushing the wall weekly for a few weeks. Didn't get the condition improved.
Highly appreciate if anyone could give an idea.

Test levels today;
FC 5.0
CC ~0
PH 7.8
TA 110
CYA ~80 (very subjective though with the TF100 kit)
CH 700~800 (cannot replace water due to water restriction ...)

photo link:
Shared album - Eric Yang - Google Photos

 

[YippeeSkippy]

Ok, When you feel the stained area is it rough?? Your CH is high so scale is a definite possibility. With CH high we like to have you keep your pH on the lower end of normal range to help counteract the calcium. Try to go to 7.2-7.4.

Other wise we ask you to perform some quick tests here- hold a chlorine puck up against the stain for a few minutes. Does it lighten it? If so that suggests its organics.

Next- take a handful of cheap Vitamin C tablets and put them in a sock and bang it up to crush them up a bit. Now hold that sock full of Vitamin C against a different area of stain than where you held the chlorine puck. If it lightens it it suggests you have metals in the water.

How are you sanitizing the pool? Do you ever use algaecides?

Yip

 

[pooldv]

The Vit C test will tell you if it is iron if it lightens the stain. Another test is to put dry acid in a sock and rub it on a stain. This will clear up a copper stain or calcium scale.

I can't see a pic in your post. You can upload the pic to photobucket, copy the IMG code and paste it in your post. That will embed the pic in your thread so everyone can see it.

 

[Eric_yang]

The Vit C test will tell you if it is iron if it lightens the stain. Another test is to put dry acid in a sock and rub it on a stain. This will clear up a copper stain or calcium scale.

I can't see a pic in your post. You can upload the pic to photobucket, copy the IMG code and paste it in your post. That will embed the pic in your thread so everyone can see it.

Thanks for the advice. Can you see the pic now? I found it was too big to paste.


- - - Updated - - -


Thanks I'll try. I never used any algaecides to sanitize the pool. In the past 4 months the water has been clear till now with TFPC.

Ok, When you feel the stained area is it rough?? Your CH is high so scale is a definite possibility. With CH high we like to have you keep your pH on the lower end of normal range to help counteract the calcium. Try to go to 7.2-7.4.

Other wise we ask you to perform some quick tests here- hold a chlorine puck up against the stain for a few minutes. Does it lighten it? If so that suggests its organics.

Next- take a handful of cheap Vitamin C tablets and put them in a sock and bang it up to crush them up a bit. Now hold that sock full of Vitamin C against a different area of stain than where you held the chlorine puck. If it lightens it it suggests you have metals in the water.


Yip

 

[MarianParoo]

I would also mention that it looks like your FC is low for your CYA: Pool School - Chlorine / CYA Chart

 

[Eric_yang]

Hi Marian

Thanks for the note. The issue is that I really not sure how accurate of my CYA test. The TF100 test kit requires me to drop the combined liquid until "cannot see the black mark at the bottom of the CYA viewing cylindra". I cannot define to what extent is regarded "cannot see", as I was feeling the a dark spot was always there, though very blur...
Anyways, I'll add more bleach as it should bring no harm.

I would also mention that it looks like your FC is low for your CYA: Pool School - Chlorine / CYA Chart

 

[pooldv]

Here is what the cya test looks like, https://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=36

Yes, I can see the pic now. Are the stains raised and rough?