Water balance for plaster spa

[SlowRocker]

Hey All,

I’m a bit confused about water chemistry for our spa which is attached to the pool (currently closed for the winter). I’ve read the sticky by Nitro and I’m not sure if it applies to what we have especially when it comes to the suggested CH level.


I have been balancing the water similar to how our pool is maintained except I keep the TA around 60ppm to help offset the quick rise in pH. Now I’ve read that TA should be kept around 50. But, 50 and even 60, isn’t in the recommended range on PoolMath . If I change TA to 70, I’m adding in muriatic acid every 3 days or so.

Should I forget what’s recommended by PoolMath? Go with the spa setting instead of a tradition pool setting? If I did go with the spa setting, wouldn’t the low CH have an effect on the plaster?

Latest numbers are:
FC - 7.5
CC - .5
pH – 7.6
CH – 310
TA – 60
CYA – 40
Borates – 0 (will be adding in once I figure out what ideal numbers are)

Currently, I have the SWCG winterized and manually chlorinating with bleach (too difficult to dial in a perfect setting with the fluctuating temps) . Min. and max. temps are between 72 and 100. Sitting in the corner of the equipment shed is a big ol bucket of boric acid ready to be added (not all) once I get the numbers straightened out.

Suggestions/Recommendations? Anything would be greatly appreciated. Thanks!

 

[JoyfulNoise]

If you're going to maintain this spa separately form the pool, then you should increase your CH a little (maybe go to 350ppm), add 30ppm borates and keep your pH on the high side (never lower than 7.7). Having higher pH in the spa won't affect the comfort level. As long as you maintain your spa water temperature at or above 70F, your CSI will be ok. Adding the borates helps with the pH rise but it does make the CSI more negative which is why I think 30ppm would be better than 50ppm. Unfortunately with a plaster spa, you have to be more careful with the chemistry. Temperature is important too - once you go below 70F, the water gets more corrosive. So if you plan to let the spa go at some point (maybe the gas/electric bill gets too high ), then you'll want to bring the TA back up or simply turn the spa over into the pool so that the two waters equilibrate.

 

[SlowRocker]

Thanks Matt. Was really hoping you'd jump in. So, my "ideal" numbers for pH, CH, TA and borates are as follows:

pH - above 7.7 (will shoot for 7.8)
CH - 350
TA - 50
Borates - 30

The heater is set to a minimum temp of 72 and I throw on a solar cover after we're done every night. Temp, so far, stays well above 70 by the time we're heating it again. When the pool opens again in Spring, I will switch back to the pool numbers until we close again in the fall. I usually drain the spa and refill when we close anyway to get salt out.

I noticed you didn't mention FC. I usually shoot for a number around 7. Do you think that's appropriate or should I lower it?

 

[MarianParoo]

Did you add those borates yet?

 

[SlowRocker]

Yes, added 20oz of boric acid yesterday, and will check later on today to see where I'm at. Numbers prior to addition were:

FC - 8.5
CC - 0.5
pH - 7.8
TA - between 50 and 60
CYA - 50

I didn't get a chance to check CH so I'm sure I'm still a bit low. Will add a bit to bump it up to 350 later. Even with my numbers off a bit, I'm still well within the range for CSI. Hopefully, this will settle my quick rising pH problem in the spa and I won't have to check the water daily.

 

[MarianParoo]

So how goes it? How is your CSI? Maybe Matt will take a peek with all new numbers.

 

[Patrick_B]

Not that it isn't important, or can't be an issue but CSI isn't that often a huge concern for most situations, most of the time.

Mostly wanted to say you're doing better than you think with getting a handle on the numbers, and that's a most beautiful shot in the dark! Nice.

 

[SlowRocker]

So how goes it? How is your CSI? Maybe Matt will take a peek with all new numbers.

Looking pretty good. I really like the way the water seems to "glisten" in the sun. I haven't received my TA and CH refills, yet, so I'm going to have to use the previous number for TA and guess on CH since I added a couple of ounces over the weekend.

FC - 6.5
CC - .5
pH - 7.8
TA - 55
CH - 350?
CYA - 50
Borate - 50

Overshot the borates a bit but I'm still within the good range on CSI, between -.11 and .13 per my temperature range.

 

[SlowRocker]

Not that it isn't important, or can't be an issue but CSI isn't that often a huge concern for most situations, most of the time.

Mostly wanted to say you're doing better than you think with getting a handle on the numbers, and that's a most beautiful shot in the dark! Nice.

Thanks Patrick. Been awhile since I've heard from you. Hope all is well. That picture was taken last winter and it's one of my favorites. So far, all has been going pretty smoothly.

BTW, the Dolphin M5 you recommended many moons ago has worked out great. Thanks again for the push.