What is this?!

[amber82181]

We had an incredibly hot summer (Houston, Tx) with numerous days over 100 degrees in a row, started seeing this light blueish stain on the pool plaster in September 2023 and has been hanging around since then. Anyone have an idea of what it is? FYI: It doesn’t come off with brushing. Help!

 

[amber82181]

POOL SPECS______________________
15k gal, gunite, 500 sq. ft., pump: pentair whisperflo 1.5hp, filter: 48sq ft FNS Plus (fiber clear media), sanitizer: rainbow inline 320 (poolife chemicals), ozone: ozone joe water purification, booster pump: pentair 3/4 HP (LA01N)

 

[mknauss]

Welcome to the forum.
Do any of the 'Poolife Chemicals' have copper in them?

 

[amber82181]

Thank you! and yes, I made a switch to this version of poolife tabs below that appear to have copper!

"Poolife MPT Extra 3" Chlorinating Tablets, all in one chlorine tablets" (New member link removed by Jim R.)

 

[mknauss]

The stains are likely copper.

 

[JamesW]

Drop a vitamin C tablet on a spot to see if there is any reaction.

Get a Jack's Stain Id Kit.

Do you have a heater?

Do you have an ionizer and an ozonator?

 

[JamesW]

Looks like typical turquoise copper stains.

The stains can also turn black.

Can you post a full set of chemistry readings?

What test kit do you have?

Can you open the filter to show the grids?

When is the last time that you cleaned the filter?

Was there any blue or turquoise stains in the filter?