Puzzled by Pool Stains-Baqaucil

jnmahone

Member
Mar 31, 2021
17
Central Texas
Hello Everyone,
I have a 16' x 32' rectangular Intex pool (about 14K gallons), vinyl liner, sand filtration. We purchased this last summer and maintained clear water throughout the peak season using a regimen of 27% strength peroxide oxidizer, biguanide sanitizer, and extra algaecide on a limited basis. The pool was initially filled with city water trucked in, but then topped off here and there with water from our well which is quite hard. The pool sat uncovered and untreated for about 4 months during Texas' colder months, w/ pump circulating about 8hrs a day, accept during freezing temps. During this time we noticed stain buildup on the walls and outer perimeter of pool. Figuring it was just algae, I shocked the pool with peroxide waited a day, then added startup doses of algaecide waited another day with the pump recirculating. Then I did a couple initial vacuums removing loose debris and leaves. During these initial vacuums, I noticed that while debris was being sucked up, the scrubbing action during vacuuming was not successful getting back to completely clean vinyl and in many locations there was almost impenetrable thin crust or scale. I did a couple more rounds of algaecide, waiting 24 to 48hrs followed by vacuuming and scrubbing. I am at a point now where no progress is being made and the perimeter stains are still present. I can remove stains with my finger nail or something very abrasive, but they do not respond to the bristles on brush cleaning attachments, and since this vinyl I am not sure I want to go more abrasive than this.
Thinking this might be metal staining due to our hard water, I tried the vitamin-C tablet test using about 10 tabs in one spot and I see very little response over an hour time (maybe slightly lighter). I used 10 localized tablets just in case the higher level of peroxide was cancelling out the ascorbic acid; (Not sure if that is a thing). I left a chlorine puck on the stain for 3 to 5 minutes and no response; no lightening of the area, no nothing. I sprinkled some ALUM in a small area just because I had some on hand. After it dissolved there was little indication of it doing anything, but when I ran a bristle brush over the area, a little bit of the scale came off, but nothing ground breaking. I tried rubbing an orange on some areas with no success. I do not have any noticeable calcium deposits anywhere, but thats not to say it could not have settled on the floor in the winter months. Anyways, before spending money on stain removers, I wanted to see if anyone had some thought on how to remedy or identify this. Is this metal staining, calcium buildup, algae that needs continued treatment and weeks to properly break down, or just scrubbing with something extra abrasive that is still safe for vinyl?
Attached is a pic of the algae scale/crust that I was able to get off during the vacuum process, but most of it does not budge. You can see little nubs where it conformed/embedded to all the little indentations in the vinyl liner.

Regards

Current water properties:
alkalinity: 120
ph: 7.0 to 7.2
peroxide: 60 ppm
biguanide: 0 to 5 ppm (have not treated with this yet)

63873029664__F30794A3-4424-4265-990C-7AAD78715116.JPG
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: Well, you seem to have quite the pool cocktail going on there. Baqua pools are a bit tricky with some owners who continue to use them, while others are happy to convert to chlorine as we prescribe here at TFP. Typically, organic stains would show some change with the chlorine tab/puck. Iron should react the Vitamin C almost immediately, especially if applied directly to the stain. If the stain, grew darker from any of these methods, it could be copper which would be possible from all the algaecides added if they were copper-based. On top of all that, you have hard chunks that can be removed from the liner. Then there's the baqua itself. Let me ask you the following:

1 - Do you plan on staying with Baquacil, or do you plan to convert to chlorine?
2 - Beside peroxide, algacides, and baqua, have you added any other chemicals?

The other thing I would like to do at this point is tag @Leebo since he converted and has some good pointers about baqua pools. While waiting, please update your signature with all of your pool details to include how you test your water. We may have more questions for you as we progress.
 

Leebo

Admin
TFP Expert
LifeTime Supporter
Jul 21, 2011
10,462
Eastern Ohio
Pool Size
25000
Surface
Vinyl
Chlorine
Liquid Chlorine
Are you on a well or do you use city water?
 

jnmahone

Member
Mar 31, 2021
17
Central Texas
Welcome to TFP! :wave: Well, you seem to have quick the pool cocktail going on there. Baqua pools are a bit tricky with some owners who continue to use them, while others are happy to convert to chlorine as we prescribe here at TFP. Typically, organic stains would show some change with the chlorine tab/puck. Iron should react the Vitamin C almost immediately, especially if applied directly to the stain. If the stain, grew darker from any of these methods, it could be copper which would be possible from all the algaecides added if they were copper-based. On top of all that, you have hard chunks that can be removed from the liner. Then there's the baqua itself. Let me ask you the following:

1 - Do you plan on staying with Baquacil, or do you plan to convert to chlorine?
2 - Beside peroxide, algacides, and baqua, have you added any other chemicals?

The other thing I would like to do at this point is tag @Leebo since he converted and has some good pointers about baqua pools. While waiting, please update your signature with all of your pool details to include how you test your water. We may have more questions for you as we progress.
We use Aquasilk products, but I assume they are basically the same as Baquacil, maybe even made by the same company.
We were successful using the peroxide, buiganide combo last year and hope to continue with those products.

I did add 4 lbs of ALUM after the first round of algaecide and scrubbing since that stirred up lots of debris. Rather than filter all that, I used the flocculant properties to help pull all the floating debris to floor for my next round of vacuuming. Thats it though no other chemicals but the peroxide and algaecide (both aquasilk products), and one round of ALUM.
 

jnmahone

Member
Mar 31, 2021
17
Central Texas
I should note the stains did not start until we left it idle and untreated for the winter months so the amount of chemicals in the water should have been minimal.
Also so it is clear, the timeline is as follows:
- New pool successfully treated with Aquasilk regimen from June 2020 through October 2020
- Pool left recirculating daily but no chemicals added from Nov. 2020 through Feb 2021. Algae and Stains developed during this time.
- Went to open pool in March 2021 with initial shock amounts of peroxide and algaecide thinking that would allow me to remove the stain buildup, but have not been successful after multiple wash/rinse/repeats of scrubbing, algaecide, and vacuuming. NOTE: No new stains have developed just can't seem to remove the existing ones.
 
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JamesW

TFP Expert
Mar 2, 2011
23,856
That bright yellow is really strange.

What happens if you put a drop of acid on some of the scale?

Can you post a list of all of the chemicals you have added?

Not the brand name, the actual chemical ingredients.
 

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jnmahone

Member
Mar 31, 2021
17
Central Texas
That bright yellow is really strange.

What happens if you put a drop of acid on some of the scale?

Can you post a list of all of the chemicals you have added?

Not the brand name, the actual chemical ingredients.
Drop of acid, what kind are referring to?
hydrochloric, oxalic, ascorbic, citric ......

Chemicals used last summer:
peroxide (H2O2) : 27% strength
biguanide: 20% poly hydrochloride (hexamethylenebiguanide) + 80% other ingredients (some of which I have been told by the rep are peroxide and algaecide)
algeacide: 50% didecyl dimethyl ammonium chloride + 50% inert ingredients (the SDS makes mention of different alcohols)

Chemicals used this spring
peroxide: 27% strength
algeacide: 50% didecyl dimethyl ammonium chloride + 50% inert ingredients
1 dose of ALUM which is aluminum sulfate

There may be a more specific MSDS for the aquasilk product line.
 

JamesW

TFP Expert
Mar 2, 2011
23,856
Possibly a biguanide compound of some sort.

Did you ever add biguanide without good circulation and thoroughly brushing the pool?

Did you ever add biguanide and any other chemical at the same time or on the same day?
 

JamesW

TFP Expert
Mar 2, 2011
23,856
Looking for a bubbling reaction which could indicate carbon dioxide from calcium carbonate.

See if it will dissolve in distilled water and then test the water for biguanide.

Does it have any smell?
 

jnmahone

Member
Mar 31, 2021
17
Central Texas
Possibly a biguanide compound of some sort.

Did you ever add biguanide without good circulation and thoroughly brushing the pool?
Not that I can recall
Did you ever add biguanide and any other chemical at the same time or on the same day?
I believe I added biguanide and algeacide a couple times on the same day toward the end of the 2020 season September / October. These were maintenance doses not startup doses. Pump was circulating 8 to 10hrs a day.
 

jnmahone

Member
Mar 31, 2021
17
Central Texas
Looking for a bubbling reaction which could indicate carbon dioxide from calcium carbonate.

See if it will dissolve in distilled water and then test the water for biguanide.

Does it have any smell?
James your recommendations gave me an idea. Since I did not have any hydrochloric acid on hand, I went with what I did have; CLR(calcium, lime, rust) remover and white vinegar. I dropped the vacuumed flakes into the solutions and both elicited a bubbling response. The CLR bubbled on the surface of each flake and broke it down into smaller chunks. The vinegar promoted bubbles that rose to the surface like a fizzy drink, and broke things down a bit, but at a slower rate.
Both off gassed, with a smell slightly more pungent than their starting smell. So perhaps I have hardened calcium maybe even lime from our well water that mineralized with embedded algae. What do you think?
 

JamesW

TFP Expert
Mar 2, 2011
23,856
Possibly calcium carbonate with various other compounds mixed in.

Did you add any calcium chloride or sodium carbonate?

Try dissolving in distilled water and then test using a biguanide test.
 

jnmahone

Member
Mar 31, 2021
17
Central Texas
Possibly calcium carbonate with various other compounds mixed in.
I will note the vinegar was much less effective at breaking down the flakes than the CLR. However since my VIT-C test was a flop I assume the rust (iron) component of this experiment to not be factor. Maybe the CLR is more concentrated or acidic than vinegar?
Did you add any calcium chloride or sodium carbonate?
No ... the only other thing I added twice last summer that I forgot to mention was dry acid (sodium bisulfate) to lower ALK and PH.
Try dissolving in distilled water and then test using a biguanide test.
Ok I will try and get back to the forum when I have results.
 
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