Blue substance in our pool

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Hi All
I am new to the forum so please excuse me if I get the etiquette wrong.
I look after a pool in a school.
Since I have been here I have managed to get the Dolphin pool cleaner working. Every time I take the filters out of the cleaner and rinse them out I am left with a blue residue in the sink. (see photos)
I have asked a number of people if they know what this is and have not found any answer that I think is satisfactory.
Before I started using the cleaner in the pool there appeared to be a jelly like substance that was see-through but more of a milky white not blue. When I managed to scoop some out of the pool this then looked blue in the net and when squeezed turned to what looked like soggy blue wiper role.
Every time I get about the same amount out of the pool (Once a week I use the Dolphin).
Hope my descriptions make sense.
The pool appears to be crystal clear.
The pool is a lined pool, if this helps.

Kind regards and thanks in advance
 

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Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
21,153
Bedford, TX
B,

I have no idea what that is... Tell us more about what chemicals you put in the pool.. How is the pool sanitize?

Let's see if Matt has any input.. Calling @JoyfulNoise

Thanks,

Jim R.
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Hi J
The pool is an indoor pool 12000 gallons.
This pool is chemically topped up using a dosing system at the moment we are using "Calcium Hypochlorite granules" and "Sodium Hydrogen sulphate granules".
The pool runs 2x800 gallon filters, filled with sand, these were relined with Fibre Glass about 3 years ago from what information I have received. We backwash each filter once evert 2 weeks on an alternate basis so each week we do one of the filters.
We use a Dolphin x2 pro gyro.
Started looking after the pool in October 2020.

Please let me know what else you may require.

Spoke to our pool guy 30 years experience he has no idea. He tested it for me and said it was not toxic.

Cheers Burn
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Hi James
The pipework is all plastic and the only chemicals we add are the ones above. The pool is lined so some sort of PVC type fabric.
Heating is via a stainless steel veined heat exchanger.
I cant think of any other parts that could be copper.
I do not know what the balance tank is lined with but I cant see them using a copper lining?

Cheers Burn
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,704
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Please post pictures of your equipment setup. We need to see all the plumbing, how it is routed to the equipment and how your dosing system is installed relative to your equipment.
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Hi Matt

The system is huge (in my opinion) the dosing system is situated in 2 other rooms.
1 acid and 1 chlorine.
 

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JamesW

TFP Expert
Mar 2, 2011
23,915
Our Algaecide has copper sulphate as an ingredient?
That will do it.

You also have several metal components that are probably alloys that are partly copper, iron and other metals.

Look inside the pump strainer housings to see if the insides are corroding.
 
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JamesW

TFP Expert
Mar 2, 2011
23,915
The pool is an indoor pool 12000 gallons.
There's no way that the pool is only 12,000 gallons with that system. Is that a typo? Did you mean 120,000 gallons?
Spoke to our pool guy 30 years experience he has no idea. He tested it for me and said it was not toxic.
If he has no idea what the substance is, there's no way that he can conclusively say that it's not toxic.

What test was done to test for toxicity?

I would think that a person with 30 years of experience would be familiar with copper causing a blue, green or turquoise color.

In my opinion, it's probably copper from the algaecide.

How much algaecide has been added?

Why are you using algaecide for an indoor pool?

What are all of your chemical levels?
 
Last edited:

JamesW

TFP Expert
Mar 2, 2011
23,915
This pool is chemically topped up using a dosing system at the moment we are using "Calcium Hypochlorite granules" and "Sodium Hydrogen sulphate granules".
Calcium hypochlorite creates a lot of insoluble products that will precipitate out as various types of residue.

I would not use sodium bisulfate (dry acid) to lower the pH. You don't want to add a bunch of sulfate to the water.

You should use hydrochloric acid instead.
 
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JamesW

TFP Expert
Mar 2, 2011
23,915
Where the calcium hypochlorite is added will create a high pH and high calcium solution that will create insoluble precipitation including copper in the mix.
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
There's no way that the pool is only 12,000 gallons with that system. Is that a typo? Did you mean 120,000 gallons?
Sorry 120000 Gallons
If he has no idea what the substance is, there's no way that he can conclusively say that it's not toxic.

What test was done to test for toxicity?
I dont know what tests but if you dont know what it is you can test for toxic materials
I would think that a person with 30 years of experience would be familiar with copper causing a blue, green or turquoise color.
Thats why I am nonplussed
In my opinion, it's probably copper from the algaecide.

How much algaecide has been added?
Recommended for the pool size 19 litres
Why are you using algaecide for an indoor pool?
Because when I arrived there was black algae in the pool
What are all of your chemical levels?
Acid 7.5
Chlorine 2.2
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Hi James

What worries me is that this is the same amount I take out every week. If I had to crush it down to a fine power I would be getting about a cup and a half out every week.
Algaecide was added once in November.

Cheers Burn
 

JamesW

TFP Expert
Mar 2, 2011
23,915
I suspect that the calcium hypochlorite is probably causing the copper to precipitate out in small batches with the insoluble compounds in the calcium hypochlorite.

It's probably going to happen for a while until the copper level goes down.

I would switch away from calcium hypochlorite and go to sodium hypochlorite.

I would stop using the dry acid and switch to muriatic acid.
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,704
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Test the residue with HCl. Just put some in a glass mason jar and add a few drops of muriatic acid to it. If it fizzes, it’s calcium carbonate. If it doesn’t fizz much but slowly dissolves over time (minutes to hours) it’s a mix of calcium carbonate and calcium sulfate. The blue coloration is likely from copper and metal compounds being dissolved by your acid feeder.
 

Burnhard

In The Industry
Mar 18, 2021
13
South UK
Thanks for all your replies and suggestions.
I guess I was hoping for a "I've seen that before and its ............"
I will try HCI and see if I can change the type of acid i use and take it from there😏 As soon as I can.
I will get back to u all with my findings🙂
 

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