Scaling on Tile

[Kit]

After draining our in-ground spa (to pressure test for a possible leak), I noticed some white scaling on the tile surfaces. Although the deposits were easily removed with a ScotchBrite pad, the spa builder said that this was likely due to either too high of a salt level or a calcium issue. Since I had consistently kept calcium hardness at 375 ppm, I assume that I eliminated calcium imbalance as the culprit. That suggests, therefore, that the salt level has been too high.

Although I have tried to keep the salt level around 3,400 ppm, I must admit that the various readings (from both the SWG & the Taylor reagent test kit) seemed to vary widely on a day-to-day basis. Before that was obvious, I likely overreacted to a falling salt level & added more salt trying to stabilize the level at 3,400 ppm.

In order not to "over-salt" the water in the future, would it be advisable to maintain a lower salt level (say, 2,800 ppm)? I want to maintain a sufficient salt level for chlorine generation, yet avoid the issues stemming from too much salt.

I would truly appreciate your thoughts on this. Thank you kindly.

 

[pooldv]

Salt doesn't leave a line on the tile. It is most likely calcium scale. Oddly, the Calcium level has little to do with the potential for scale. PH and TA are much more important factors in determining scale potential. Post a full set of test results. It is important to keep PH between 7.5 and 7.8 in a plaster pool. Especially with SWG as it will tend to push PH up.

To prevent scale keep your CSI between -0.3 and 0. PoolMath will give you the number, tweak PH and TA to move the number. Keeping your CSI slightly negative will also help prevent scale in your SWG cell and make it last longer. More here, Pool School - Calcium Scaling

 

[Kit]

Maybe I am misusing the term "scaling". This is not a hard deposit line along the waterline. I am referring to a thin whitish film on the horizontal 1" tile on the spa bench, as well as the tile that is underwater in the skimmer cavity. Might this be the result of too much salt? I am diligent about keeping pH within the 7.5 - 7.8 range. My target range for TA is 60 - 80; but admittedly it tends to be closer to 90.

Last set of test results:

FC = 5
pH = 7.8
CH = 325
TA = 90
CYA = 60 (target = 70).

Admittedly, I have not checked the CSI; but will do so from now on.

Thank you so much for your help.

 

[JoyfulNoise]

Does your spa run all the time at an idle temperature (say, 90F) and then you ramp it up as needed? Or do you just spot heat it every time?

Warm water will scale faster than cold water and a turbulent spa will have much higher pH levels associated with it. It sounds like what your seeing is simply evaporite - the water level rises when people are in the spa and it is running and then it drops back down to a lower level when the water is idle. Each time the water does that, it leaves behind a thin layer of evaporated salts (sodium chlorine, calcium carbonate, organic scum, etc). Unless the tile surface is "sealed" with a tile sealant (kind of like what they do in showers to prevent tile haze), the water will wet the surface of the tile and a very thin layer will stick to the tile. That layer evaporates and leaves behind what your are seeing. In technical terms, it's very similar to a Langmuir-Blodgget film.

You could clean the tile and then apply a sealant by lowering the water level and sealing the tile. But most tile sealants are designed for wet environments, not really submerged applications, so I'm not sure how long a coating like that would last underwater. One way to clean it off easily is with a spray bottle filled with diluted muriatic acid (5 parts water to 1 part acid). Lower the water level, spray the acid on, let it bubble a little and then wipe it clean with a damp cloth or sponge (dampen in a bucket of distilled water).

 

[Kit]

Matt: The pump runs 4 hours daily for filtration & chlorine generation. The set temperature is 81F. Prior to use, I will ramp up the temperature to 98F. The white film that I noticed is not evident along the waterline.; but rather on the bench which is always below water. As I previously mentioned, because of inconsistent salt level readings I might have been overreacting & adding additional salt when it was not necessary. That gives rise to my question whether I should establish a lower target salt level (e.g. 2,800 ppm) to avoid over-salting in the future.