Help With Stains on Salt Pool

[VikingPoolMan]

We recently took over a pool - it's a 20,000+ gallon salt pool. When I took the pool over, the salt level was around 1800ppm which was too low for the unit to work properly (it has a 40k purechlor system which requires salt to be in the range of 3500ppm - 4500ppm). In any case, it's a beautiful pool with a relatively new surface (about 3 years)... the surface is very similar to a pebble tec finish (home owner wasn't sure the exact type of surface). The home owner is VERY particular... she fired the last pool company because she was getting small calcium spots on her pool. When I took the pool over, I lowered the PH to 7.2 and the alkalinity to 60 to make the water a little more aggressive... then I added a sequestering agent. In a week or so, I was able to brush off the calcium spots. Also, I slowly added salt to the pool to bring it back up to normal level (3850ppm now).... over the last few weeks, a very lightly colored white-film (almost looks like sunlight) is spreading on the bottom of the pool. I'm keeping the water aggressive and brushing it down hard. I put acid directly on the film but it doesn't really do much... The home owner is not happy, however, the water chemistry is perfect so it's hard for her to blame us..... My guess is the pool's surface does not react well with salt and some type of scaling is happening due to high saline levels in the water. Also, now I'm seeing those calcium spots reappear (even though the water is aggressive and the calcium level is 270)... very strange problem and nothing seems to help to take off the film. The pool builder (who did the surface 3 years ago) recommended to the home owner to drain the pool half way and dump 8 gallons of acid in the water. I would rather not do that.

Stain treatment is not really my strongest area of expertise.... hopefully, someone here has a better idea of what this is and/or how to handle it. Thanks!!!

 

[onBalance]

If this is a re-plaster pebble finish, and the calcium spots are scattered and random, then that problem might be calcium nodules.
As for the white-film, if acid isn't removing it, then it probably isn't calcium scale. Does the white film cover the pebble or is it only on the cement portion?
It doesn't make sense to drain the pool half-way and then pour acid in. Bad advice.

 

[VikingPoolMan]

If this is a re-plaster pebble finish, and the calcium spots are scattered and random, then that problem might be calcium nodules.
As for the white-film, if acid isn't removing it, then it probably isn't calcium scale. Does the white film cover the pebble or is it only on the cement portion?
It doesn't make sense to drain the pool half-way and then pour acid in. Bad advice.

Thanks.... the white film covers everything (about 1/5 of the bottom of the pool). I thought it was just sunlight hitting the bottom of the pool at first. Then it grew like a cancer... keeping the water aggressive & wire brush (and the sequestering agent) has seemed to help (a little). And it's strange the calcium spots are returning during this time. I agree the film is not calcium - I put acid directly on it and it didn't really do anything. Since the only significant change I've made to the pool was increasing the salt level, I'm assuming that's the culprit. Other than the scaling problem, the pool is beautiful.

In any case, not sure what else I can do for this pool.... thanks for help.

 

[JoyfulNoise]

I didn't want to jump in with crazy theories but any chance there was heavy use of dry acid in this pool? Calcium sulfate scaling is unusual but with enough sulfates in the water it can happen. And I don't believe that calcium sulfate is susceptible to acid dissolution like calcium carbonate scale would be.

That said, the simplest answer is best. I wonder if the plaster wasn't properly started up or if the previous service companies were using a lot of no drain acid washes and now your just dealing with a weak plaster surface that allows for the constant emission of calcium oxide and the formation of scale. Again, just some simple thoughts on the subject as I am no plaster expert.

 

[VikingPoolMan]

I appreciate all your insights. When I took the pool over, the only problem was the calcium spots. I made the water more aggressive and that helped with the spots. Then, all of a sudden, the white film started to appear like a cancer over the bottom. The only thing I did to the pool (apart from making the water more aggressive) was increase the salt level. However, since this is a "new problem" under my watch, it makes the home owner suspect that it's somehow my fault. Honestly, I'm getting tired of dealing with the pool.

To answer your question, I don't believe any dry acid was used - but I can ask. I told the lady that my best guess was how the surface was applied/started up and for some reason it doesn't like higher salt levels.... And, the calcium spots are returning now (which is also strange). Is there anything else I could be doing to remove this scale or do you believe it was just poorly applied plaster? Thanks again for your help.

I didn't want to jump in with crazy theories but any chance there was heavy use of dry acid in this pool? Calcium sulfate scaling is unusual but with enough sulfates in the water it can happen. And I don't believe that calcium sulfate is susceptible to acid dissolution like calcium carbonate scale would be.

That said, the simplest answer is best. I wonder if the plaster wasn't properly started up or if the previous service companies were using a lot of no drain acid washes and now your just dealing with a weak plaster surface that allows for the constant emission of calcium oxide and the formation of scale. Again, just some simple thoughts on the subject as I am no plaster expert.

 

[onBalance]

If the calcium spots are actually raised (and rough) calcium nodules and are due to delamination or bond failure, it is common for them to form again and again after removing.
See this post: Calcium Nodules in pools
If that is what is going on with this pool, then that might be the more serious problem.

As for the white-film, there is also another reason for a whitish appearance to develop, and that is due to porosity of the cement. If the cement is weak and becomes leached and porous, it becomes a lighter color than a dark color plaster that contains a color pigment. But this is a 3 year old plaster job, so I don't think that is the cause either. I am at a loss regarding that issue.

 

[VikingPoolMan]

Thanks for the help... I'll read that post on calcium nodules later tonight