Little white spots all over pool bottom

[InvaderZim]

Howdy!

We have a two year-old 26,000 gallon salt water pool with Jandy equipment and "pacific blue" plaster. Last summer, we started seeing little hard white spots scattered around the bottom, interspersed with just a few larger ones. The bigger ones look kind of like bird droppings, the little ones are just sharp points. Here's a photo I took today of an 18" deep shelf (sorry about the reflections).

Our pool service company says this isn't typical scale -- they aren't sure what these are, although they believe it may be calcium coming out of the plaster. We've never had any scale or deposits at the water line, although our water is a bit hard (400ppm) and they've suggested draining 1/2 the pool before it gets warm enough to swim in to reduce that). The spots are mostly on horizontal surfaces and can be scraped off with a credit card but that would get a bit tedious for the entire pool.

We did have some problems controlling the ph last summer (when the water was warm enough to swim in), and had to add acid twice a week. The ph would range between 7.8 and 8.5. We also had to treat the water for phosphates -- got up to 1,000 ppb but now it's down to 200ppb. We have a lot of trees and the pool is kind of a mess in the fall (elms) and spring (live oaks), but we can deal with that. The little spots are the only problem -- never had algae problems at all, and the water is crystal clear. The other chemical levels are ok.

Any ideas or suggestions for additional tests would be welcome.

 

[duraleigh]

I'd say you're on the right track. High Calcium and high pH = calcium deposits.

If they'll scrape off now, I think I'd lower pH to 6.8 and monitor it very carefully to hold it there for a month or so.....brushing the spots often. Add some fill water if your fill is low enough to effectively lower your CH. Those two strategies may result in the calcium being dissolved back into solution, or, at the least, stop them from continuing to occur. Once your pool is back satisfactoery, be sure to put your pH back around 7.4

 

[JasonLion]

You really need to keep the PH from going above 8.0, particularly with high calcium levels.

You should post a full set of water test results. That will help give us a better idea of what might be happening.

Phosphate remover is mostly a waste of money. If you maintain appropriate chlorine levels you won't get algae, even if your phosphate level is quite high. Phosphates wouldn't have anything to do with the white spots in any case.

 

[InvaderZim]

Thanks for your replies -- I haven' t been able to find the last set of water test results (a few weeks old) but I'll go to the pool store this week. I did check the pH and it was 7.6-7.8 (hard to read, but I did put in some acid to lower it to 7.4). The chlorine generator is still turned way down to 25% (water temp about 65 degrees and free chlorine is still around 5ppm) and I suspect that the chlorine generator has something to do with the rapidly rising pH we see in the summer -- I've seen comments about chlorine generator aeration raising pH on this forum (have a lot more reading to do -- great resource!)

I'll talk to our service company about lowering the ph for a while -- is a pH of 6.8 at the point where it may damage the plaster or equipment? What about using the spa with that kind of ph? Or might draining 1/2 the pool (it's full now) to lower the hardness and maintaining a lower pH (like the suggested 7.4) be sufficient?

Is it odd that there aren't any calcium deposits or scale on the tile at the waterline? That's what seems to confuse our pool service company.

Good to know that phosphate isn't that significant. That will save me a few bucks. Thanks!

 

[JasonLion]

Lowering PH below 7.0 does have some risks, I believe that is why duraleigh said it would need to be monitored very closely. The idea is that if calcium has been scaling then changing the PH so calcium is dissolved back into the water can reverse the scaling. If you go too far with that process it can damage the plaster and there is also a slight risk to the copper heat exchange coils in many heaters.

To avoid future scaling, without trying to reverse any existing scaling, simply requires keeping PH at 7.8 or lower, keeping TA from getting too high, and not letting CH get any higher.

SWGs do have a tendency to cause PH increases. This can be particularly severe if TA is high and can usually be brought under control by lowering TA. PH can also rise if you have plaster that is less than one year old.

 

[InvaderZim]

Cleaning out my inbox and I realized I'd never replied to this message, so I figured I'd post a followup: we've been religiously keeping the pH in the 7.2-7.8 range, but it requires adding acid twice a week. So the pool service company does it on Wednesday, I test on Saturday and when the water was still warm, I'd have to add a couple of pints every weekend. That does seem to have stopped the progression of the little white spots -- they haven't completely gone away but I think there might be fewer of them. I think the sudden outburst we had was due to the pH spiking.

Our service company suggested that we get some sandpaper designed for wet/underwater use (apparently it's sold by Home Depot and use that to smooth out the little bumps in the spa. I haven't yet tried that but I'm considering it. A pumice stone works nicely but doesn't go very far and I also wonder about releasing the calcium in the stone into the water. Is that a legitimate concern, or is it just not enough to matter?

Anyway, I can live with adding acid twice a week. Thanks for the advice and sorry for the lack of followup.

 

[Guest]

You might want to read this thread on water balance for SWGs.
viewtopic.php?f=21&t=3663
Posting a full set of test results can help us make suggestions on how to better combat your constantly rising pH but I have a few suspicions as to what might be going on.

You might also want to consider adding borates to your water to help with the pH rise once you get your other water parameters in line (if they are not borax won't be that much help!)
viewtopic.php?f=21&t=3663

Third, you might want to consider getting rid of the pool service, getting a GOOD test kit, and taking control of your own water! That is the only way to really ensure that your pool is kept up properly! (and I do commercial pool maintenance during the summers so I know a bit about what REALLY goes on! )

Finally, as far as the 'white spots' in your pool, there it almost sounds like they may be calcium nodules

http://www.poolhelp.com/onBalanceCalciu ... lletin.pdf

or soft spots.

http://www.poolhelp.com/emails.aspx

Both of these issues have less to do with water balance then they do with how your pool was constructed, specifically how the plaster was applied and cured.

From your description they sound more like calcium nodules.

 

[spishex]

I agree that it sounds like nodules. A cheap drywall pole sander and sanding sheets will do the job.