Calcium precipitate from SWG?

[rootusrootus]

I have a fairly new (less than a year) Nordic Retreat MS hot tub. At the time I bought it, I also bought a Saltron Mini and I've been using that since day 1. A couple months ago I noticed some white sandy particles in the bottom of the hot tub (at each seat, like they're coming out of the vents, and on the floor). I chalked it up to people bringing in dirt to the tub, and figured it would be gone when I did my next drain & fill. Well, I did that yesterday, all completely fresh totally clean hot tub, added salt/calcium/CYA/muriatic acid/chlorine per PoolMath calculations, and let it heat up. Just went to get in an hour ago and there's a bunch of the white sand again (and some darker particles, too). Almost all of it directly below where the Saltron Mini is hanging, but a little here and there in the various seats too. And I can feel some of the grit on the Saltron Mini itself.

Is this calcium carbonate precipitate? Why am I suddenly seeing it now, and in great quantity? The pH was really high after I filled it yesterday, but I brought it right down to 7.5 with muriatic acid before putting the cover on. Is there something I could be measuring and adjusting to prevent this?

 

[Texas Splash]

The only white products I can think of would be calcium, salt, or undissolved granular stabilizer. To see if it's calcium, try to grab some of it, place it in a pile, and pour some vinegar on it to see if it fizzles. Muriatic acid would give that reaction as well. If there was scale on the SWG's cell plates, it's possible some of it has been flaking off.

 

[Mdragger88]

Your ch is a little higher than necessary, you seem to have added quite a bit of calcium chloride at once (450ppm worth)
that can do it when combined with high ph.
Ch of 150 is generally plenty for a stand alone spa.

 

[rootusrootus]

Thanks for the tip on the CH. My target in PoolMath is pretty high, I'll dial it down. And come to think of it, I wasn't really adding CH early on, because I was unsure if I should put any at all in a hot tub. So the timing makes sense. I can easily dump a bunch of water and fill it again, then readjust the chemicals. Got lots of salt inbound, I just bought 5 more bags of salt for the big pool (I had to drain and drain and drain the pool all winter long to keep it from digging a hole from running over the top of the skimmer, we got soooo much rain).

I'll also do a quick test to verify it is indeed CH flakes I'm seeing, just to be sure.

Again, TFP comes to the rescue, you guys are the best!

 

[Mdragger88]

You may also need to clean the saltron mini cell. Since you can’t really get at it physically you will need to use a quick diluted vinegar bath if you can see scale. The bottom plastic piece on the cell is removable for you to get a good look at it first & make that call. I am not sure if the cell reverses polarity - if it does it may have already shed any scale.
Fwiw I have only 25-50 ch in my tub and it’s fine - you can go up to 150 to prevent foaming if necessary but more than that is overkill.
Your shell is plastic/acrylic so in poolmath select vinyl.