Sand in pool

[nefretrameses]

I have sand forming in the bottom of my inground pool with a cartrige filter. The finish appears to be "diamond brite" and the sand that is collected by the filter after brushing has green/blue specks in it. I don't recall this happening last year (We are starting our third year of ownership). The finish is probably 5 years old. Is it time to resurface or is this a chemical balance problem?

[Watermom]

I am not sure how to help you with this question but I have asked PoolDoc to have a look for you.

Welcome to the Pool Forum!

[PoolDoc]

1. I've never worked with a Diamondbrite pool, so I can't answer with certainty.

2. Chemical imbalances do not cause you to have sand in the bottom of the pool. Sustained low pH can result in finish damage, and sand-like particles. Get some of the particles, and look at them closely to see what they are.

3. Unless your Diamondbrite finish already has "green/blue specks" in it, such specks are not from the Diamondbrite.

4. Most Portland cement based pool finishes (like Diamondbrite) do not HAVE to be replaced till they become so rough they retain algae OR so thin the gunite shows through. Before that, you MAY replace them, but it's just a matter of preference.

5. "green/blue specks" CAN be from copper flakes, if you have anything copper in your pool -- like a heater.

6. In any case, we can't really help you with your chemistry, till you get a K2006 (see Amazon link in my signature) -- test strip results, even from a dealer, simply are NOT accurate enough.

7. Meanwhile, if you use borax and muriatic acid (see link in my sig) to keep your pH between 7.0 and 7.8, any ADDITIONAL damage should be minimal. Get a cheap local OTO/phenol red (yellow/red) drops kit to test with, till the K2006 arrives.

[nefretrameses]

So I got my test kit and had the following results:
FC: 18 ppm
ph: <7.0
TA: 75
CH: 175
The chlorine is way high and ph is low.

So I took a water sample to two pool stores. The first said my FC was 1.9!! The second said "high" and that my ph test would not be accurate with such high chlorine. I backed my chorine system way off. (cartridge filter with continuous chlorine (3inch tabs).

I looked at the "sand" It is defenitely from the pool finish. The Taylor iinformation said low ph will etch the finish.

I'm going to get my chlorine level down and redo the ph test.

John

[BigDave]

We'll need a CYA level to know how high FC is. But, high FC usually makes pH read high. I would raise the pH with Borax straight away because <7.0 could be much lower.

[nefretrameses]

Retest on 6/20 (am) after adding 1 box borax the previous evening:
FC: 13.0 ppm
CC: 0 ppm
ph: 7.9
TA: 80 During this test the sample turned green and then to yellow vs. red
CH: 200 The sample was "pink" rather than red
CYA: 80 I'm a little confised about what "disappears from view means. I assume that if I can see the dot at all it has not "disappeared from view".

Today the pool has never looked better.

Still trying to determine if the sand (which I'm sure is coming from the pool finish) is the result of low ph etching the surface or if the pool just needs to be re-finished. (not sure when the current finish was applied - at least 5 years)

I am brushing a couple of times a day so hopefully the accumulation of sand will stop with the right ph.

[Watermom]

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

[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.

[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.

[Marin]

They make underwater polishing equipment (not even close to cheap) for that purpose.

I thought I'd mentioned earlier, maybe I dreamed it, or it's the fatigue & allergy meds, but throw away that SS brush. It's slowly damaging your finish (maybe even causing "sand"). Get a nice high quality nylon brush. SS brushes are too aggressive for nice finishes. Older pools with a bad surface and algae? Go for it. Otherwise no.

[nefretrameses]

I mostly use a nylon brush for routine cleaning, but I have the SS brush for the occasional heavier need. The surface is at least 7 years old and a little rough in spots. The previous owner said refinishing after 10 - 12 years would not be unexpected. Don't know if that's right or not. If so, I'd expect to refinish in 3 - 5 years. I'd probably want to do it anyway to fix the "pockets" that in in floor pop-ups are in.

[Marin]

Really depends on care. Some folks need refinishing after 7 years, some go 20+ years.

When you replaster, make sure your contractor uses the infloor collar extensions to raise the heads up level with the new plaster.

[nefretrameses]

Would it be unreasonable to expect a refinisher to grind down around the in floor fittings and main drain., etc. so the new finish is flat ?

[Marin]

When we replaster a pool we set a new main drain cover and use the infloor collar extensions to keep things flush. Other items, like lights and return fittings, we chip out around those so we can bring the plaster back flush with the fitting.

[nefretrameses]

Thanks. I'll keep an open mind. I suppose if I want it done a certain way that is not standard practice, it becomes a cost/ benefit trade off.

[Marin]

In the past we have chipped out around the infloor heads to bring the plaster flush, by we have to go back about 2' around each one to do it well. Not worth it when the collar extensions have no effect on the performance.