Mystery of the white powder in pool

[uman]

Hello,

Several years ago I noticed deposits of fine white powder in the spa, pool floor and filter.
I have collected and saved the powder out of the spa with a Aqua-tech vac and have measured one pound over one year.
This represents about one third of the total deposit (spa + pool + filter). So I estimate about 3lbs powder in one year.

I had a pool leak Technician perform a leak check of the pool and he found no leaks, with a air pressure leak decay test.
The pool looses about 1/8" water per day in hot Florida sun; this is typical for pools this area.
The powder is pure white, hard, granular and very fine and is not water soluble.

The Tech suggested the powder was coming from within the spa PVC pipe system, which he suspects is flex PVC (but not confirmed).
He thinks the flex PVC (or rigid PVC) is deteriorating and releasing the powder.

My next test is to clean pool/spa/filter and and attach flex tubes with dark color fabric strainers to each jet and spa spill over to isolate the source.

In-ground 13,000 gal pool 12 yrs old
Pool is Gunite with no signs of deterioration
Spa is Fiberglass with no signs of deterioration
Salt water chlorination at setting 30%
Filter cartridge fiber type (not DE type)
Water analysis indicates no problems
The pool is plumbed to discharge pump full volume into spa and spill into pool

This mystery must be solved, I think I am on borrowed time.
Please offer suggestions and experience.

Thanks for reading....Jeff in Florida

 

[tlevy]

Calcium??? Assume you have never taken it to a lab for analysis.


90,000litre, IG vinyl, 1/2 HP Tristar pump, Sandfilter, Aquarite T-15 ASG

 

[JohnT]

Do you ever shock the pool? What product do you use? How about pH control?

 

[uman]

Calcium; umm. Is there a simple way to test if this is calcium? Could calcium build up this volume of mass?

Shock the pool; I rarely shock the pool. How would this effect this condition? It is a salt pool, Should this be included in a test?

-Jeff

 

[JohnT]

Calcium; umm. Is there a simple way to test if this is calcium? Could calcium build up this volume of mass?

Shock the pool; I rarely shock the pool. How would this effect this condition? It is a salt pool, Should this be included in a test?

-Jeff

Many dry chemicals won't dissolve well and end up on the bottom of the pool.

 

[poolnoob.ca]

a drop of dilute (5-10%) muriatic acid would make it fizz if it was calcium according to this: http://geology.com/minerals/acid-test.shtml

p.s. but calcium would dissolve in water wouldnt it? (unless high pH was causing it to scale)

paging dr chemgeek to the deep end

 

[uman]

A solution of 10% muriatic acid to water by weight was mixed.
The mystery powder was sprinkled on solution surface and a violent reaction occurred.

I believe this eliminates sand or PVC as the powder.
Could it be Calcium? How could this be?

-Jeff

 

[uman]

A solution of 10% muriatic acid to water by weight was mixed.
The mystery powder was sprinkled on solution surface and a violent reaction occurred.

I believe this eliminates sand or PVC as the powder.
Could it be Calcium? How could this be?
-Jeff

Here is the water test from last month:

FC: 4.0 ppm
PH: 8.0
Acid demand: 2
TA: 95 ppm
Calcium Hardness: 250 ppm
Stab: 30 ppm
Total dissolved solids: 3900 ppm
Salt: 2600 ppm

-Jeff

 

[Divin Dave]

Not sure if my questions will help or not, but throwing them out anyway.

First, you mention all your water parameters are good. Im hoping that since you've been a member since 2011, the testing results were made with a good test kit, and not a pool store test? Can you post the test results?

There may be something there that my be evident to the chemistry experts. Reliable test results could help us determine what your CSI is. Low CSI can be corrosive to plaster. High CSI can produce calcium scaling, which you seem to have none of.
If its plaster dust, it also fizzes in Muriatic Acid

Next, have you checked your filters to see if they are caked with this stuff? Do you use Trisodiumphosphate the soak your filters? or any other cartridge filter cleaner?
Is it possible its hard calcium deposits being released by caked up filters?

 

[zea3]

Your pH is too high and your calcium is on the lowest end of the acceptable range. Do you keep a log of your test results that would show changes in the calcium level? Which part of Florida are you located?

When I plugged your test results into http://www.troublefreepool.com/calc.html it showed a potential to develop calcium scale. Try scratching the plaster with a fingernail below the water line and see if you are able to scratch any of it off.

 

[uman]

The pool is located in Central Florida, Merritt Island.
The pool surface appears to be in excellent condition and will not scratch at the waterline or anywhere else.
I believe it is the original surface. I owned the pool for 4 years now.
I have the water tested at local pool store (Pinch-a-Penny).
The calcium level has been stable between 230-275 for the lasts 12 months.
My filter is canister type and it collects some (about a cup every 4 months), but is not caked.

I would be very interested to learn what the white powder is. How could this be determined.

-Jeff

 

[Divin Dave]

You could have a chemical analysis of it performed. Google up chemical analysis testing in your area, or perhaps call up your county extension agent and ask if they know a lab to do it.

 

[ozzy47]

Also I would not rely on pool store results, get yourself a proper test kit.

 

[zea3]

How often do you brush the pool?

 

[uman]

The pool is brushed about twice a year.
Could it be residue from the surface? It seems to be in very good condition.
I will get a good test kit and do it myself.

-Jeff

 

[JamesW]

Most likely it's calcium carbonate from the plaster aggregate. This is common on very old plaster. Not sure why you would be getting it like this. Did you get regular marble aggregate plaster?

Also note that plaster should be brused weekly.

 

[uman]

Most likely it's calcium carbonate from the plaster aggregate. This is common on very old plaster. Not sure why you would be getting it like this. Did you get regular marble aggregate plaster?

Also note that plaster should be brused weekly.

I am not the original owner and do not know what type of plaster coat the walls of the pool.
Brushed weekly; oh my, this is alarming.
I will perform a complete cleaning of the pool surfaces, spa and filter and then brush weekly and report back after several weeks.

Thanks for all your help Tlvey, JohnT, Poolnoob, Divin Dave, Zea3, Ozzy47 and JamesW.

-Jeff in Florida

 

[ozzy47]

Just keep us updated, and once you get a proper test kit, post the results.

 

[chem geek]

A solution of 10% muriatic acid to water by weight was mixed.
The mystery powder was sprinkled on solution surface and a violent reaction occurred.

If by "violent reaction" you mean it dissolved with lots of bubbles (gas) then it is most likely to be calcium carbonate. If you were to instead add a small amount of acid to the powder, it would fizz or bubble, again because this converts the carbonate into carbon dioxide gas.

Your 3900 ppm TDS with 2600 ppm salt doesn't make sense. Though TDS is larger than the salt level, it's not that much larger. The "other" TDS components are mostly the TA and CH and those are not that high. Borates would be another contributor, but again, not that high.

Let's see what a real test kit tells us. If you don't have either a TFTestkits TF-100 or Taylor K-2006, get one pronto.

 

[JamesW]

Most likely the tds was reported assuming a 442 standard solution, which would have the same conductivity but a different ppm than NaCl. I suspect that the person testing the water had a dual meter such as the myronl 512T5D Pool Meter and set it to salinity to test the salt and 442 to test tds without knowing that that was not the correct thing to do.

Rereading the original post, I see that the pool is 12 years old. I thought it was newer. That fits better with what you're seeing.