Calcium

[JamesW]

Did the algaecide contain copper?

The small black spots look like black algae.

The larger dark spots look like copper.

In any case, the water looks murky and needs a lot of work.

Typically, you would clean the filter and then do a full SLAM.

However, if you have a lot of copper, you're at risk for serious stains if you SLAM.

 

[Texas Splash]

Not a new pool, 1993...so 26yrs old.

That is important as well. Depending on FB pool sources in yoru area, some FB pools "may" have been made with small amounts of calcium in that time. Not sure if you would have any literature available on your pool, but you might reach-out to some local dealers to see if pools commonly installed in your area back in the early 90's were fabricated with calcium.

 

[AussieSwimmer]

CSI

Did the algaecide contain copper?

The small black spots look like black algae.

The larger dark spots look like copper.

In any case, the water looks murky and needs a lot of work.

Typically, you would clean the filter and then do a full SLAM.

However, if you have a lot of copper, you're at risk for serious stains if you SLAM.

Photo is old, water is crystal clear. Algaecide did contain copper. Do I confirm with test? Is there a way to remove copper stains/copper from water.

 

[JamesW]

If the algaecide contained copper, then you have copper in the pool.

Do you have a recent picture with clear water?

If the small black spots are black algae, they should scrape off with a fingernail or other non abrasive scraper.

Black algae is a blue/green mold type substance.

It's actually a type of bacteria called cyanobacteria. It's actually toxic in some cases. So, be careful with it.

Copper stains can usually be treated with sulfamic acid, but results are not guaranteed.

Removing copper usually requires a drain and refill, but that should only be done if it can be done safely.

Draining a concrete or fiberglass pool can cause the pool to pop out of the ground under certain circumstances.

A vinyl pool usually can't be drained without replacing the liner.