Water Line Tile in Spa - Cleaning Recommendations

UrbanCoyote

Member
Jul 27, 2017
12
Fulshear, TX
My hot tub/spa has a white water line residue (calcium?) deposit and I am looking for recommendations on how to clean it off. I have used muratic acid in the past with little success.

The spa is always at a constant level as it has a spillover to the pool. Normal pump operation returns a portion of the filtered pool water to the spa and the rest goes to the pool returns. My calcium is currently at 325 but historically runs around 250.

I assume this white line is calcium but I do not have this line in my pool. It is also strange because my calcium levels typically run within the recommended ranges. Could this be something leaching from the concrete, stone mortor, or grout?
Thanks in advance!
 

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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I assume this white line is calcium but I do not have this line in my pool.
It's possible the calcium ring you are seeing is related to the volatile environment to a spa itself - specifically the water temp and aeration. Those have a dramatic effect on the pH and your CSI (Calcium Saturation Index (CSI) - Trouble Free Pool). That could be why you don't see the same effects elsewhere.

For now, I would recommend posting a full set of test results for us from the spa. In the meantime, I'll ping another expert @pooldv who may have a thought or two. For the ring itself, it's always best to start light and go stronger if needed. You mentioned MA mixtures already right? With a wire brush? Other items include nylon scrub pads or even some very fine wet/dry sandpaper (600-1000 grit perhaps). Some will use a pumice stone, but as with all of these products, always test a small area first to ensure you're happy with the end result. Some products may leave very fine scratches or can even lighten the tile a bit, so be careful.

Also see: Calcium Scaling - Trouble Free Pool
 

Dodger

Silver Supporter
Sep 17, 2017
539
Silicon Valley, CA
It's possible the calcium ring you are seeing is related to the volatile environment to a spa itself - specifically the water temp and aeration. Those have a dramatic effect on the pH and your CSI (Calcium Saturation Index (CSI) - Trouble Free Pool). That could be why you don't see the same effects elsewhere.
Spa ring and no pool ring is what happens in our pool/spa combo. One of the main things I do to prevent/minimize re-occurrence of the spa ring is to bring the spa pH down to ~7.2 before heating it up. It's amazing how fast the pH will rise with bodies and air jets, so I sometimes test afterwards and add MA to the spa again before letting that water spill over in the next cycle.
 
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UrbanCoyote

Member
Jul 27, 2017
12
Fulshear, TX
I tested the water a few hours ago. I tested the pool and the spa, and they were identical (makes sense since a large portion of the return water enters the hot tup and spills over into the pool during normal circulation mode for 6-8 hrs/day). We don't use the spa that much - average 1 to 2 times per month.
FC 1.5
CC 0
pH 7.8
TA 70
CH 325
CYA 40
CSI 0.03
Temp. 73F

I added bleach and a little MA per pool math to bring FC up to 6 and pH to 7.6.
Awhile back I attempted to use muratic acid and a plastic brush with little effect. Once the water warms up a bit, I will get a stiffer brush (or similar) and try again. Just curious as to what is the cause. The pool is about 1.5 years old; the rings started forming shortly after construction. I had to consistently add calcium after it was built to keep the CH up, but it seems to have tapered off in the last 6-9 months.
Thanks for the great feedback... appreciate the insight.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Whenever we have water sitting at a certain location (like a waterline), it's quite common that calcium will try to precipitate out and try to cling to that area, especially in places where the CSI in positive. In the spa's case, the CSI shoots-up through the roof once you crank the water temp up. In addition, your pH is (was) on the upper end. Maybe not an issue for the pool alone, but in the spa could increase the potential for scale with hotter water.

Interesting about your csi reading. I'm not at home so I have to use the old PoolMath web page, but I'm getting a postivie csi of 0.12. Not outrageous by any means, but a bit different than your 0.03. As a test, if I was to lower your pH to 7.4, then the csi goes to negative -0.27 which should help to prevent calcium from trying to form. Keep in mind these numbers are based on your current temp of 73. Once I crank-up the water temp for the spa to an estimated 94 for example, your CSI shoots-up quickly to positive 0.3 (pH of 7.8), while the water with a lower pH of 7.4 stays just under negative at -0.09. Pooldv may be offline still, so I'll also ask @JoyfulNoise to chime in if he has a moment to see if I'm missing anything.
 

pooldv

Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
25,287
FL panhandle
Yes, the ring around the tile line is all about CSI. Once it gets too high scale will start to form, usually above 0.6 but sometimes above 0.3. Especially in a spa with aeration and heated water. As the water temp rises so does CSI. Keeping the CSI between -0.3 and 0 will prevent it from happening. Lowering CSI to -0.8 to -0.9 and brushing will cause the scale to dissolve back into the water. Or you can go the more aggressive route and use diluted muriatic acid and brush as discussed.

More here
 

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