Robot cleaner "collecting" salt?

[Grenademonkey543]

Hi folks,

Not quite sure what to make of this and it's somewhat of a wild guess but here goes.

I converted to a SWCG last summer and have head pretty steady salt readouts through the seasons and beyond. I got my Pentair Warrior SE (S200 clone) end of December and around February when water temps started climbing i got a low salt reading. Not a problem I said, rain must've finally done it's toll and the test strips I used paired with the read-out must've been inaccurate.

I added salt to bring levels to approx 3000-3100 ppm, however three months later, lo and behold I'm noticing the salt readout dropped to approx 2700 ppm. Now, the obvious culprit would be a leak and the auto-fill compensating - however there's a gotcha. I've started noticing the robot collecting the following "gunk" for lack of a better term over the last months.

Latest levels as of last week are good:
FC: 7
CYA: 70
TA: 50
pH: 7.5
CH: 300

I've thought it might be calcium scale that's being picked up during the waterline scrub, but it looks more like salt than anything else:





I will obviously do the bucket test to rule out a leak, but the welcoming of the robot into the family and the salt loss do seem to coincide. Any thoughts and suggestions would be greatly appreciated.

 

[mknauss]

The saturation point of sodium chloride in water is above 200,000 ppm. Your salt level is not that high, and thus, that cannot be salt.

Pile some up and put a drop of acid or vinegar on it. Does it fizz?

 

[Grenademonkey543]

Thank you @mknauss ! It was a long shot i tried some muriatic acid over dried up residue and it did fizz. So this means this is calcium dissolving ? I am hoping that with a good CSI this is not the plaster but just the lime scale.

i have ordered a K1766 for an accurate measurement of salt levels and hopefully that can give me an idea of any trends more accurately and determine if a leak is in fact taking place

 

[mknauss]

Your current test results do not show an ability to create calcium scale. Did you maintain the pH of this water over winter?

 

[Grenademonkey543]

I believe winter the pH stayed pretty consistent around 7.8 with no major intervention required. There is quite a bit of scale at the waterline though on the tile layer. Pool is at least 10-13 years old and was pool route maintained before so the history of the water chemistry beyond the 1 year i took over is cloudy (no pun intended)

As I had previously used a pressure cleaner i did not notice this as much, but do recall seeing a small ammount of similar dust in the bag last year before the salt system got installed.
I am wondering if with the waterline scrubbing feature on the robot, it’s chipping away or applying water to dissolve that scaling to the affected areas more ?

 

[mknauss]

OK -- but when I input your test results in Poolmath your CSI is below -0.6. So your water is actually quite aggressive -- and any scale in the water like you show would be dissolved into the water pretty quickly. You should let your pH rise and/or TA rise unless you know your CH will get higher soon.

Have you recently changed out water? I would expect your CH to be quite a bit higher.

 

[Grenademonkey543]

Hm.. curious indeed. Even adjusting for water temp of 92, it’s still at approximately-0.46 so I definitely have a low margin of error.
I did a water exchange last year to drop CYA. If i recall correctly, CH was around 375-400 prior to that

My TA has been consistently at 50ish for the last 8-9 motnhs. I know we shouldn’t be chasing TA and pH tends to find a sweet spot - but would this be a time to add baking soda to rise the TA?
I have no issue with pH rise due to the SWGC so obviously i counteract that when it creeps up to 8-8.2.

EDIT: Moderators, please feel free to move this to the water chemistry section since this definitely seems to not be SWCG-related (thank you @mknauss )

 

[mknauss]

We are good at leaving the thread here.

When your pH hits the 8+, only lower to 7.8, or 7.6 at most. I hate for you to add baking soda as all that will do is push you pH up higher.
FYI -- the SWCG in itself does not raise your pH. It is overall aeration.

 

[Grenademonkey543]

We are good at leaving the thread here.

When your pH hits the 8+, only lower to 7.8, or 7.6 at most. I hate for you to add baking soda as all that will do is push you pH up higher.
FYI -- the SWCG in itself does not raise your pH. It is overall aeration.

Will do. I think I've been targeting 7.2 each time I adjust higher pH, so I will target 7.8 for now and see how this fairs.

Still have to see what's up with the dropping salt readings, but we can deal with that once I get a more accurate testing method tomorrow. Since it's a string of long shots, no chance NaCl can be affected by a low CSI? ))

 

[mknauss]

NaCl effects CSI, not the other way around.