Sand in pool

[PoolDoc]

Disappearing from view means that you cannot see the dot at all. It is a tough test to read.

Unfortunately, it's the best available. The very weakest test on test strips is the CYA test. The next step up, from the disappearing dot test, requires an expensive electronic instrument to peer through the cloudy water . . . still not super accurate. And, the step up from that requires a GCMS (gas chromatograph - mass spectrograph) that runs $15,000+.

Personally, I would probably say that it's a bit of a pain to get used to, but that once you are accustomed to the test, it's not really hard at all. And fortunately, it is accurate enough to get the job done, and cheap enough to be practical.

[nefretrameses]

Update:

The pool consistently looks great. I have been maintaining appropriate balance and have raised CH to 250. The amount of "sand" has steadily decreased. Many days none is visible, although y o u can feel it on the bottom of the pool in spots. The sides feel smoother and very little material comes loose when I rub my hand on it. I'm concluding that a combination of low CH and low PH over an extended period of time softened the finish and caused it to come off. I'm considering taking my CH higher, maybe 300 or 350. I am using cal-hypo but will switch to bleach when I hit my CH target. Any opinions?

FC=7.2
TC=7.2
PH=7.6
TA=80
CH=250
CYA=80

[PoolDoc]

Might want to raise your TA a bit, instead. It's easier to adjust, than calcium.

[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.