Spa plaster rough

[gm]

We have a new pool with spa and I'm having trouble at times with the spa plaster (Diamond Brite) getting a rough, sort of sandy texture to it. It rubs/brushes off, but comes back in about a week. It seems to be when the PH gets high, and I add acis to get PH back down. The pool finish does not have this problem, and the water circulates between pool/spa.

Is this likely caused by chemical imbalance? if so, which reading (PH, chlorine, etc) is they key to watch closely?

Thanks for any input/suggestions.

GM

 

[JasonLion]

That sounds like calcite scaling. Calcium in the water will deposit on the walls of the pool/spa when the calcite saturation index gets too high. Calcite saturation depends on almost every level, PH, TA, CH, CYA, temperature, borate, and salt. You can use my Pool Calculator, see the link in my signature to calculate the calcite saturation indx (CSI), which indicates the likelyhood of scaling.

Since one of the factors is temperature, and spas are normally heated hotter than pools, it makes sense that scaling would start in the spa first. Scaling is also far more likely at high PH, since PH has the largest impact on the CSI.

You can either play around with the calculator to see how you can balance you CSI, or post all of your numbers and we can try to suggest something for you.

 

[gm]

Spa:

FC 1.0
pH 8.0
Hardness 335
Alkalinity 75
CYA 50

Pool:
Fc 2.0
pH 8.0
Hardness 335
Alkalinity 70
CYA 50

Salt was at 2800, so I'm adding 80 lbs.
The pool is around 24K-25K gallons.

 

[matj6876]

Hi gm

It most likely is calcium scale (I've had it and it's nasty).
I'd wait for the experts to comment but your numbers are fairly similar to mine (CH, CYA & TA at least) and I'm running at a pH of 7.5 - 7.7 to keep exactly that type of scale away.

Using Jason's calc you need to add about 55oz of 31.45% muriatic acid to bring your 25k Gal pool down to pH of 7.5. Good Luck

 

[gm]

thanks for the input. So, what's the best way to get the scale off? It's a bear to get off with the brush. Would a med grit wet sand paper be OK or would that damage the plaster?

 

[mas985]

I use 240-400 grit wet sand paper and it works quite well. 400 just takes longer than 240. It really doesn't take off much. Over time it could be problem if you have to continue sanding off scale so it is best to try and keep your ph down.

 

[matj6876]

So, what's the best way to get the scale off? It's a bear to get off with the brush.

Yeah - I had no joy with the brush but then again I let my scale get so bad I ended up draining and acid washing the pool. Not recommended!
If I get a bit of scale now (again it's particularly in the spa) I use pumice to remove it.