Calcium Drop in Spa With Heavy Rain Causing Rough Surfaces?

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mmcwhorter

mmcwhorter

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Jul 13, 2015
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Huntingtown, MD
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I posted this problem/issue before and never really felt like I got it solved. The original thread is below. My problem is rough marcite surfaces in the spa every spring when we open the pool, usually the Spa first. The roughness is mainly on the seating areas in the spa, with some roughness on the walls (vertical surfaces) ....and oddly: not so much on the floor. I would use a pumice stone to smooth the surface as needed for "bum comfort". It's definitely akin to sitting on 20 grit sandpaper.

I think today I may have figured out the root cause of the problem, let me know if you agree:

When I closed the pool in late Oct, the calcium level in spa and main pool was BOTH (I am certain) around 350 ppm. We have had a TON of rain here in S MD after closing pool (in fact close to 60 inches all year). Major storm systems moved up the eastern seaboard int he last 10 days....I have drained the main pool several inches twice in the last 2 weeks as the water has hit the tiles both times. So, today I decided to pull a flap off the spa cover back and take a peek at the water level there (which I rarely do). As expected, the water line was well above the bottom tile line. So I drained it back to 4-5 inches below. As I drained, I decided to measure the CH. And WOW: it was 50 ppm. So, I checked to pool CH and it was around 325 ppm.

I'm assuming there is ZERO calcium in rainwater. But even the 50 ppm in the Spa was surprisingly low.

The reason I bring up the very low number in the Spa: I am now wondering if this low CH is the problem with the rough surface in the spa every year we open. Leaching? It's mainly on the seats, not as bad on the walls the walls. But certainly having a nice smooth surface to sit on in the spa is an important attribute..... :)

So, I have a good bit of calcium chloride in storage and I looked at pool math and added about 3 pounds to my 2000 gallon spa. This should bring it up to 187 (162 +25 ppm) according to the Pool Math. I'm waiting a few hours to re-measure (the water is cold so I'll let it fully dissolve)

Am I on to something here? Have I stumbled across the real reason for the "rough spa surface" in Spring?

Here is the old thread:

Each Spring Opening I Have Rough Pitted Marcite in ONLY the Spa

I have noticed over the last three years that our "raised overflow waterfall spa" surface on both seats and vertical walls is very pitted when we pull the cover off in Spring. The rest of the pool is smooth. When closing in late Fall I take good care to balance the pool & spa.....and then shock...
www.troublefreepool.com www.troublefreepool.com
 
using a lava stone...but it's pretty tedious by hand, as it's a fairly large 6-person spa....And "solving" it is not the right word...beating it back a little to make it more livable...I wonder....would it be silly to lightly wet sand the rough seat surfaces, as I can live with the rough walls? I thought about it but have NOT tried muriatic acid...I was thinking 25% MA/75 H2)...spray it onto the top of the spa seating area using a pump sprayer, letting it sit for a few seconds, then quickly rinsing....I know I would not want that highly acidic water to go through my pump/filter/heater.
 
mmcwhorter said:
Just checked CH...and it's up to 350 ppm. I used three scoops of a 16-ounce measuring cup into a 3-gallon bucket.,..dissolved quite well.
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Does your spa overflow into the pool? That might make the CA decrease over time if you’re only draining the pool.
 
Yes, it does and I was only draining the pool.......and it was apparent that the water line was at the level of the spillover, so I really have no clue how much water went into the pool from the spa. But it does seem a bit odd to go from CH = 350 to 50 PPM since Oct 20. For what it's worth, it's back up to 350 today. And the spa water level is down 4 inches below the spillover.
 
mmcwhorter said:
Yes, it does and I was only draining the pool.......and it was apparent that the water line was at the level of the spillover, so I really have no clue how much water went into the pool from the spa. But it does seem a bit odd to go from CH = 350 to 50 PPM since Oct 20. For what it's worth, it's back up to 350 today. And the spa water level is down 4 inches below the spillover.
Click to expand...
If you’ve been getting lots of rain then the spa filling up with rain water and then overflowing into the pool would lower the CH in the spa. It does seem hard to go from 350 to 50 though.
 
Hello Duraleigh, here are the numbers: The water is probably at or near 50F, FC = 0, CC = at or near 0 (0.5???), pH off the charts above 8.2 purple like I have never seen before, and TA between 40-50....meaning that the sample changed color briefly after 4 drops, then went clear...adding the 5th drop made it a solid color change.
Since the pH was who knows how high....I added 4 ounces diluted into a 3-gallon bucket of water and poured it in. I am assuming my spa is on the order of 2000 gallons when full, it's down 4 inches below the tile.
 
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I will re-check the pH a few minutes from now.

The pool HAS BEEN fully winterized and covered around Oct 20. I have already had to drain the main pool twice due to the amount of rain since then. ...Yesterday, having a hunch about the "low calcium" causing the surface roughness, and wanted to check for the expected high water level in the spa....I popped off two of the loop-lock straps that allowed me to peel the cover back to see. Sure enough, it was over the tile. I dropped a submersible pump into the spa and brought the water line down to below the tile line, about 4 inches below....which is where I left it on Oct 20. I have one pump for the main pool and another for the spa.
 
Measured pH....wow, 4 ounces very carefully measured of 31.45 MA took it to around 6.8, maybe a little lower. So, according to Pool Math, my spa MUST be less than 2000 (closer to 1200) gallons, and of course, right now the level is down below the tile line right now. I'm going to break out a water volume calculator to see if I can better estimate the spa volume.
 
mmcwhorter said:
Measured pH....wow, 4 ounces very carefully measured of 31.45 MA took it to around 6.8, maybe a little lower. So, according to Pool Math, my spa MUST be less than 2000 (closer to 1200) gallons, and of course, right now the level is down below the tile line right now. I'm going to break out a water volume calculator to see if I can better estimate the spa volume.
Click to expand...
The calculator isn’t very accurate for pH changes more than 0.4 so don’t get hasty depending on what your target was and what your actual pH was.
 
So, here's some thoughts.........

Plaster with pH consistently wa-a-ay too low (6.6 or lower for an extended period) will likely leach from the pool surface (seat) and cause pitting and it could be localized within the seat surfaces.

Plaster with pH consistently too high can easily cause calcium scale on those same seats.

Can you tell by looking and feeling if the roughness is from calcium added on in bumps or calcium subtracted with pitting the result??
 
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I am certain that the pH level during the open seasons all has always been in the normal range of 7.2 to 7.8. However, I am assuming that when the pool is closed, the pH creeps up high. This has been validated because this is the first time I’ve ever measured it after closing the pool and receiving lots of rainwater. There is no possibility that the pH has ever been super low in the spa. Going forward, I will keep an eye occasionally on the pH and calcium until I open in the spring and then take a good look at the surface to answer your questions. Thanks for your help. It’s really appreciated and happy new year!
 
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