Large crystals in my pool

[hans.oskam]

Hello,

I live in Spain and have a pool 6 mtr. x 12 mtr. x 1,5 mtr. and fill it with the water from my well. On the walls and floor I have many sharp Crystals (see photo). No one can tell me here what these crystals are and with what (chemical) I can remove them and what I have to do to prevent it. I let analyse the water from my well at an official laboratory and put the results with this message.
I often check the pool water put clorinetablets in it for the right level and about 2 times a season I have to put some PH-minor in the pool.
On the picture you see the crystals on the tiles and joints. The tiles are glassmozaik 2 cm. x 2 cm.
Please Help!!!!

 

[Bama Rambler]

Is that a fiberglass pool?

 

[Jamison04]

Could it possibly be sulfur deposits forming? From the results you posted of your well water it has an insanely high sulphate level. Sulphur rich water around here forms a white cutsty layer on anything left in the water for long periods of time. Just a guess?

 

[Praterma2]

I just want to beat chem geek in. 1700 ppm seems a little high for SO4 conc. What does anyone think about CaSO4 as the precip? I am just a novice on the board, so I would like to know what more experienced members of the board think.
Thanks

 

[hans.oskam]

Is that a fiberglass pool?

Maybe my pool is a secret fiberglass plant

 

[Praterma2]

Sorry Jamison, I took too long in posting and did not update to see your post. I know there is a well established history with CaSO4 precip in industrial applications (Desaline.com/articoli/5080.pdf for example) but I just was not sure in a pool based environment. The crystal picture is nice . Confirmation should be cheap and easy.

 

[onBalance]

You are correct.
I have seen this before in Tucson Arizona and Las Vegas Nevada pools. Had the crystals analyzed and were determined to be mainly calcium sulfate crystals in composition. The pool in Tucson was drawing water from a well with high contents of sulfates.

 

[hans.oskam]

You are correct.
I have seen this before in Tucson Arizona and Las Vegas Nevada pools. Had the crystals analyzed and were determined to be mainly calcium sulfate crystals in composition. The pool in Tucson was drawing water from a well with high contents of sulfates.

Hello and thanks for the reply.

But what did they do to clean the pool end wath tot prevent the crystals??? The strange thing is that at no other place where we use the same water we have these crystals. The only difference is that we use in the pool chloridetablets and some times the PH-minor.

 

[duraleigh]

I have never have seen anything like that on the forum so cannot help OP.

However, there may never be a better testimonial as to the disadvantages of filling your pool with well water.

If you are setting up or building a new pool, before you fill it from your well, search this forum for the hundreds of posts about disadvantages of well water.

 

[onBalance]

Calcium sulfate crystals form due to high contents of calcium and sulfate. Perhaps the tablets you are adding are calcium based (calcium hypochlorite) which adds calcium to the water. The pH minor product you add is probably sodium bisulfate, which adds sulfates to the water. If your well water also has a high content of sulfate and calcium, and with evaporation of the pool water over time, then that combination would lead to the crystals forming.

Unfortunately, these crystals are very difficult to remove. Muriatic acid won't work to dissolve them. Only very warm (actually hot) water dissolves them and is a slow process.

 

[chem geek]

The chemical report on the water shows 485 mg/L calcium, but in Calcium Hardness units of mg/L calcium carbonate that would be 1211 ppm! The bicarbonate is shown as 277 mg/L HCO₃^- which in TA units would be 227 ppm (there's a factor of 2 for TA since carbonate counts twice relative to bicarbonate). As others have noted, the 1690 ppm sulfate is very high. The TDS from all of this is around 4300 ppm.

The calcium carbonate saturation index is over +0.6 (the high ionic strength lowers it from what it would otherwise be) so that's high by itself. The calcium sulfate concentrations are about double their precipitation amount (i.e. their saturation index is around +0.3) and it was probably higher before the precipitation (crystal formation) began.

That's really lousy water to start with. I'm not sure if you have reverse osmosis or water softening options in your area.