What is this white stuff?

[neirbot]

See the attached photos -- what is this white stuff? This is only happening near the spa spill-over, and no where else around the pool -- it's an eyesore on an otherwise perfectly looking pool (thanks to this site).

Here are my numbers:

FC 4
pH 7.5
TA 50
CH 250
CYA 40

 

[JamesW]

Probably efflorescence from water leaching through the cracks at the spots where the scale is building up.

As water seeps through the concrete, it dissolves minerals and deposits them on the outside of the cracks.

 

[neirbot]

Thanks for the quick reply. I'll look up how to get rid of it, but any tips would be appreciated!

 

[Flying Tivo]

You can scrub them away with a mild acid solution, but after that your best bet is to try to seal the rocks with some type of sealant. Probably reapply once a year.

Felipe

 

[ajw22]

Just an observation since you posted your numbers. With CYA 40 your FC target should be 5-7 without a SWG.

 

[JamesW]

The water is probably leaking from the spa through the wall, which would indicate that the spa is not water tight.

The efflorescence will probably continue to build up unless you make the spa watertight.

 

[neirbot]

You can scrub them away with a mild acid solution, but after that your best bet is to try to seal the rocks with some type of sealant. Probably reapply once a year.
Felipe

Thanks -- very helpful.

Just an observation since you posted your numbers. With CYA 40 your FC target should be 5-7 without a SWG.

Good catch -- it's usually near 7, often higher during the summer. We don't get too much direct sunlight on the pool in the winter, so I have a little more flexibility with the FC levels.

 

[ajw22]

Good catch -- it's usually near 7, often higher during the summer. We don't get much direct sunlight on the pool in the winter, so I have a little more flexibility with the FC levels.

A bit higher is always better for FC levels then lower.