salt-like residue?

[JasonAshley]

I have a tanning ledge with a bubbler and I've noticed a salt-like residue that settles on the ledge after several days of not sweeping. It isn't salt, but is grainy like salt/sand and white in color. My calcium content is on the high side and I've had issues with scaling on the tile/grout line, as well as in my salt cell.

pH 7.6
FC 6
TA 110
CH 400-450
CYA 60

Since joining the site and educating myself more, I've learned that a high TA has a tendency to promote scaling. I'm working to lower the TA. I don't think it is calcium residue, just noting that I realize my CH is a little elevated. It appears that the residue is coming from the bubbler, since I don't really see it anywhere else other than the tanning ledge. Has anyone experienced this or know what this may be? Thanks for any help.

 

[chem geek]

Welcome to TFP!

Splash-out evaporates the water leaving the salt minerals behind. It might be calcium carbonate or it might be sodium chloride salt or some combination. Collect some of it and add a few drops of acid to it and see if it fizzes. If it does, then it contains calcium carbonate. If not, then it's more likely to be sodium chloride salt. Since you have a "salt cell" (saltwater chlorine generator) your salt level is probably around 3000 ppm so would be the dominant solid material left after evaporation. This is not uncommon.

To reduce scaling on the tile/grout line as well as in your salt cell, you are right that lowering the TA should help with that. You could lower your TA to 80 ppm or even 70 ppm. I wouldn't change your CH level in spite of what the Recommended Levels say -- your 400-450 ppm CH should be fine if you get your TA lower by following the Lower Total Alkalinity procedure.

 

[JasonAshley]

Thank you for the response. I forgot to list the salt level in my previous post, but it's 3200 ppm. I may have not explained the situation well, but it's on the the ledge which is actually about 8 inches deep, so it's not from evaporation. It doesn't taste salty at all (not sure how smart it was to taste it, but I figure that was the quick poor man's way to eliminate one choice). I will try your suggestion of dripping some acid on it to see if any reaction occurs as soon as it builds up again.

I was a little concerned about the CH level, but I will not worry about it and will follow the steps to lower TA you provided. Thanks again, I find this site to be an invaluable resource to any pool owner.

 

[ouachita]

Any chance it's DE?

 

[JasonAshley]

Pretty sure it's not DE. This residue reacts with muriatic acid and I tested a few drops on DE and got no reaction with the acid. From what chem geek said, if it fizzles with acid (and it does), it contains calcium carbonate. Is this different than the calcium scaling I get on the grout, which I read is also calcium carbonate? Also, what causes it to precipitate into this grainy form that settles on the bottom of the pool. This doesn't really seem to affect the water quality as it remains clear, but does cloud things up when I sweep it off the steps, etc.

 

[chem geek]

No, it's the same calcium carbonate as on the grout. Since your CSI with your water parameters (assuming 3000 ppm salt) is only slightly above 0, I suspect that the precipitate on the floor are calcium carbonate flakes formed in the saltwater chlorine generator (SWCG). The hydrogen gas generation plate is very high in pH so will tend to form calcium carbonate scale. Every certain number of hours, the polarity of the plates in the SWCG reverses and any calcium carbonate buildup on the plates is sloughed off since it is now a chlorine generation plate which is low in pH.

As I wrote earlier, lowering the TA level should help reduce this problem. If that isn't enough, then you could consider adding 50 ppm Borates to the pool as that would cut down the amount of pH rise in the SWCG roughly in half.