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.