Sand in pool

[nefretrameses]

But isn't CH more related to possible surface damage that TA?

[PoolDoc]

Actually, by far the most important factor is pH, or rather, pH + temperature. After that, it's alkalinity, and then calcium. There is a sort of exception: because of the way the process of dissolution or precipitation works, if either alkalinity or calcium are near zero, or even less than 60 ppm, THEN their significance goes way up.

Water, in the presence of calcium materials, will NOT stay near zero in calcium long!

[nefretrameses]

Thanks Doc. It's interesting though. It's been about 6 weeks since I got my Taylor test kit and was able to get my water balance in some kind of control. I also assumed PH was an important factor, and based on the advice I got here, I immediately raised it, and have maintained it, in the appropriate range since I got my test kit. But I still had "sand" in similar amounts compared to before I sought your advice. I finally found a source for CaCl, since it's pretty rare in Florida, (Fastenal) only two weeks ago. Once I had it, I raised CH from 180 to 250 over a three day period. Since then, it seems that the amount of "sand" has lessened. Of course this is a perception, since I have not measured the amount in any way. The smoothness of the sides also improved since raising CH (again a perception). Maybe this is just the result of having the PH in the proper range for that 6 weeks rather than the result of having the CH raised for 2 weeks. Or maybe a combination of both?

I don't think either CH or TA ever got anywhere near zero, or even less than 80 at any time. My fill water has a TA of 180 and CH of 110.

[PoolDoc]

I'm not aware of any careful studies of pool surfaces, but from what data I have seen, and from my own field experience it's my judgement that if:
(a) the pH remains between 7.2 and 8.0;
(b) the alkalinity remains above 80;
(c) the calcium remains above 100;
then you are unlikely to see erosion of the pool surface . . . caused by water quality.

BUT . . . there's a huge controversy in the pool industry due to problems that appear in concrete surfaces -- plaster (Marcite) + all the other newer surfaces, like DiamondBrite, etc -- with blame by applicators being directed at chemistry, and blame by pool service guys (responsible for chemistry) being directed applicators.

Again, there are no indisputable studies. But it appears to me that there are LARGE variations in surface application quality, and that poor surfaces will deteriorate even in good water. Some of the blame appears to rest on variations in material quality, but much seems to rest on applicator skill and dedication. Unfortunately, it's very hard to define either what makes up "high materials quality" or "professional application technique".

The only real test seems to be that of time: applicators with a decade-long track record of successful and durable applications are MUCH to preferred than those with less time or history.

[nefretrameses]

Thanks, I get it. Certainly one of your three conditions were violated in my pool for an unknown length of time. The best I can do at this point is keep my water balanced and see if there are further improvements in the amount of "sand" I get. I'll raise the TA a bit and adjust to get a fairly neutral saturation index - definitely non-negative.

I can't speak with any certainty about the type or quality of either the material or applicator, since they were before my time. I know the surface was re-done since the pool was built in '85. It's a quartz aggregate of some type. Some of the in-floor pop-up's for my in-floor system now sit in "pockets" created when the finish was applied. I would have expected the old finish to be ground away in these areas so that they were fairly flat. I think that's an indication of the "applicator quality". I agree with comments made by you and others that the quality of the applicator is the most important factor.

Thanks again for all the great advice. You and you other Mods have made pool ownership much more rewarding.

[PoolDoc]

Glad we could help!

[Marin]

Sorry for coming in late on this one. Only had time to skim the 2 pages, so if I've overlooked too much please ignore me.
First off, if it's truly sand, it's not coming from your pool finish. There are no plaster type finishes that use sand. I could be wrong because I'm not familiar with them all, but that's my educated response.

A few years ago we replastered a pool and the guy started seeing sand in the bottom. He accused us of messing up his sand filter. The equipment pad was 25' away and we'd never touched it. After a lot of arguing & investigating, we found out he was using some bargain basement chlorine tabs that had sand filler in them. Chemicals desolved in the water, leaving behind sand. Just a thought.

Another scenario is if you have sandy soil and a leak in your return lines, it could draw in sand and deposit in your pool. I think that's very unlikely.

Third idea, which I've asked of others in this situation before, is if you have kids and a sandbox.

[nefretrameses]

Coming in late is no problem for me.

"Sand" is the best term I could come up with. It's really quartz crystals (i.e. sand) but is includes green and blue particles that are the same color as the "specks" in the finish. I'm not sure what tradename the finish is since it was before my time, but it's an aggregate of quartz crystals - mostly white, but with blue and green crystals in it as well. If it was just sand, I'd be looking for an external source, but the presence of the green/blue particles (in what I see on the bottom of the pool and what I wash out of the cartridge filter) convinces me it's the pool finish. Also, if I brush with a SS brush, I can get a small pile of the stuff below the brushing area.

I was using Tri-chlor tabs from Sam's Club (which I believe are a recommended brand if you are going to use Tri-chol); but I have switched to Cal-Hypo (while I raise my CH a bit) and Liquid Chlorine - so it's not that. No sand filter or kids with a sand box, but it is sandy soil for sure.

Like I told Doc, my pH was below 6.8 for an unknown length of time and CH was 180 or less as well - before I found this site.

I'm hoping having my water balanced on the slightly + side of the SI scale will eventually stop this from happening. It does seem to have slowed.
John

[PoolDoc]

It's really quartz crystals (i.e. sand) but is includes green and blue particles that are the same color as the "specks" in the finish. I

That pretty much narrows it down, to dissolved pool surface.

If you maintain your water, the rate of deterioration will slow, but won't immediately end. The reason is, aggressive water conditions penetrate into the finish, weakening the matrix that holds the quartz particles. Where the matrix dissolves completely, the particles are immediately released. But where the matrix is only weakened, it may be some time before those particles shed.

FWIW, I'm pretty sure some of those surfaces can be refinished merely by regrinding them -- if the remaining surface material is thick enough. Marin would probably be able to either confirm or correct this, and possibly point you in the direction to carry it out, if it's possible.

[nefretrameses]

Thanks Doc & Greg.

It makes sense that aggressive water is the root cause. Hopefully the damage isn't "fatal". I'll keep brushing and maintaining my water balance.

Our swim season will end sometime in mid or late October. Would it be of any benefit to raise pH or another factor so my SI is even more positive during the winter? The pool stays open.