Any connection between SWG and calcium deposits?

[SoCalBoo]

Here is my current water chemistry, stable for about the last year:

FC 5-6 ppm
CC 0
TA 90-110
Ph 7.2-7.4
salt 3200
cya 40-45
cal 480-500

22,500 gallon inground, concrete, grey plaster, poolpilot swg, minimax heater, pentair 1.5 hp for pool, 2.0 hp for spa jets. DG filter.

I have been getting decent calcium deposits on spa spillway tile for the last few years. I have always assumed it was the high cal level. My fill water is 200-220...pool is about 2 years old. Entertaining significant drain and refill currently.

I covered the pool once it dipped below 80 in late october. I also wanted to see if sunlight on a covered pool would eat up less chlorine that the uncovered pool, and if so, how much. Well, I turned off the SWG and added a .75g of ultra bleach in early october, and I didn't have to add anything until this weekend (FC dipped from 6.0 to 4.0). I figured $1 of chlorine for close to 2 months of operation was a good deal.

But then I took a look at the spa spillway. Virtually no calcium deposits were present. i had cleaned them off back when I covered the pool, but haven't done anything to them since. Typically, there would be a fair amount (4-6 quarter sized deposits) within 2 months...but virtually nothing.

Has anyone heard of anything, scientific or anecdotal, about worsening calcium deposits by using an SWG (or the reverse)?

And for those who will tell me to drain and refill, I know. I am thinking about it. New pool...many have warned me to wait for the plaster to get a few years of cure on it before you drain.

[waterbear]

My question is did you have the pump running the same time and the splliover operational when you covered the pool? If you did not then there is your answer as to why no scale deposits. The only other reason I can think of a SWG increasing scale deposits is that it can cause the pH to rise and if this is not closely monitored and corrected on a regular basis BEFORE the pH rises too high then it creates conditions that are more likely to form scale deposits.

Ph is the single most 'important' factor in the formation of scale deposits. In other words, it takes a smaller change in pH then any other factor to determine if the water is going to be corrosive or scale producing. It takes much larger changes in calcium levels, temp, etc. so, IMHO, pH is the factor that needs to be watched, all other things being equal. (I am purposely oversimplifying this. If anyone wants to discuss the various saturation indices formulas I will gladly meet them in the 'china shop' . )

[SoCalBoo]

Waterbear...pump run time has been constant since mid summer. I intended to put that in my 'facts' but neglected to.

My pool has been very quick to change ph (upwards). I've always attributed that to the SWG. I usually need to add about a pint a day, and have needed to do so since startup two years ago. Now in the summer, when the SWG is turned up because of more chlorine eaten up by sun, I have to add more muriatic.

Short and long of it is highly unusual for me to have a ph of anything other than between 7.2 and 7.5.

But don't get me wrong. I am pretty darn happy to not have nearly as much of deposit to clean up. And the kicker is that my SWG cell is likely to last a fair amount longer when it is turned off 4-5 months per year.

[waterbear]

My pool has been very quick to change ph (upwards). I've always attributed that to the SWG. I usually need to add about a pint a day, and have needed to do so since startup two years ago. Now in the summer, when the SWG is turned up because of more chlorine eaten up by sun, I have to add more muriatic.

Short and long of it is highly unusual for me to have a ph of anything other than between 7.2 and 7.5.

Try dropping your total alkalinity to about 70 ppm, and when you add acid shoot for a pH of 7.6. You might find that this gives a a better pH stability with the SWG operating. Also, I have had excellent results by adding 50 ppm borates to the water. You can do this with such products as Proteam's Supreme or Bioguard's Optimizer but if you are cheap like me you will do it with 20 mule team Borax! See this thread:
http://www.poolforum.com/pf2/showthread.php?t=4712

Aslo, what type of SWG do you have? You seem to be running your CYA on the low side and this can also contribute to pH instability by causing the cell to work more than it really needs to. Most manufacuters recommed a CYA of 60-80 ppm (one I know of recommends 80-100 ppm and one I know of recommends 50-80ppm ) and there has been an excellent discussion on this board as to why this is most likely a good idea!
http://www.poolforum.com/pf2/showthread.php?t=4495
I test a lot of pool water every day i'm at work and have a lot of customers with SWGs besides having one myself. I see fewer problems in the pools that have the CYA in the manufactuers recommended range than in the ones that try to run it lower. This emperical evidence is enough to convince me that follwing the manufacturer's recommendation in this area is a good idea! Ditto on running the TA on the low side. I have found that when the TA is dropped to around 70 ppm the acid demend tends to go down. Chemgeek has given an excellent explanation of this in another thread
http://www.poolforum.com/pf2/showthread.php?t=5379

Hope this helps.

[SoCalBoo]

Waterbear,

I've got a poolpilot digital. Love it. Works like a charm.

I'll try running the TA in the 70-80 range. I'll also shoot for 7.6 on the Ph. I'll get some borates in the pool as well (by the way, what are 'borates', how do I test for them, and is there any website that can tell me how much 20 mule borax I need to add to get to the 50 level? will bleachcalc do it?)

I've been running my cya kind of low for the swg to try and sneak up on the 'ideal' level and not overshoot. while I'm not having water chemistry problems per se (with calcium level where it is, I kind of expect to have deposits and have accepted that fate), I do recognize it could be better. so I'll try creeping up on 60ppm to see how I do. I believe the poolpilot digital sWG recommends 60-80ppm CYA. I was hoping to get by with a lower FC level...maybe I need to worry about this less and more about my TA/Ph/CYA, since I haven't had a measurable CC level in a longtime.

Thanks again for the help.

[waterbear]

Waterbear,

I'll get some borates in the pool as well (by the way, what are 'borates', how do I test for them, and is there any website that can tell me how much 20 mule borax I need to add to get to the 50 level? will bleachcalc do it?)
Bleachcalc has an error in the borax calc to achieve 50 ppm. The thread I posted above from the china shop "The Great Tetraborate Experiment" http://www.poolforum.com/pf2/showthread.php?t=4712 does tell towards the end how much 20 mule team and muriatic acid you need to add so I would suggest rereading the whole thread carefully. I know it's long but there is a lot of good stuff in it as Richard (Chemgeek) and I worked some things out!


... I do recognize it could be better. so I'll try creeping up on 60ppm to see how I do. I believe the poolpilot digital sWG recommends 60-80ppm CYA. I was hoping to get by with a lower FC level...maybe I need to worry about this less and more about my TA/Ph/CYA, since I haven't had a measurable CC level in a longtime.
Shoot for about 70 ppm. People have gotten so afraid of CYA these days....from not thinking it was important if it got too high to almost thinking of it as the antichrist and an evil that needed to be avoided at all costs! he benefits will be longer cell life, less energy consumption, more stable pH (and therefore less possibiblty of scaling conditions occuring), no 'dead spots' of understantized water, etc. How about we trust the manufacturers for once. They might actually have a clue as to how their product is supposed to work!
Thanks again for the help.

Hope this is helpful!

[chem geek]

Evan's (waterbear's) advice is excellent and will address the pH rise you are seeing and the amount of acid you have been adding. The part that doesn't make much sense to me are the calcium deposits on the spa spillway tile. With the numbers you posted I did two things (in my infamous spreadsheet) to see if I could figure out when scaling might occur. I first used a high spa temperature of 104F since higher temperatures lead to more scaling. Then I saw what sort of pH would be needed to get scale and though "balanced" water would have a pH of around 7.3, scaling normally wouldn't occur until you got to nearly 7.8. And yes, the indices that calculate this stuff are controversial so enough said about that.

So I have two thoughts about this. First, is when you startup in the spring, if you are willing to experiment then before you lower your TA and add Borax see when your pool/spa is adding deposits again. Then, test your spa water when this occurs. Perhaps the aeration and high temps of the spa have raised its pH quite high. If that is true, then the things that waterbear suggested should help reduce the scaling problem. Of course, even if you test and things look normal, waterbear's advice is still good to slow down the pH rise and reduce your use of acid and should be tried anyway to see if it eliminates this scaling problem.

My other thought is that perhaps this isn't scale but is something else. At first I thought it might just be evaporated salt, but this is a spillway and not splash-out on coping. Anyway, those are the random thoughts I had...at least you've got a good plan from waterbear that is sure to address some and probably all of the issues you are having.

Richard

[SoCalBoo]

Evan's (waterbear's) advice is excellent and will address the pH rise you are seeing and the amount of acid you have been adding. The part that doesn't make much sense to me are the calcium deposits on the spa spillway tile. With the numbers you posted I did two things (in my infamous spreadsheet) to see if I could figure out when scaling might occur. I first used a high spa temperature of 104F since higher temperatures lead to more scaling. Then I saw what sort of pH would be needed to get scale and though "balanced" water would have a pH of around 7.3, scaling normally wouldn't occur until you got to nearly 7.8. And yes, the indices that calculate this stuff are controversial so enough said about that.

HMMMM. Interesting. I will tell you that I haven't used the spa much at all recently. In fact, if it gets used more than one a week during summer, and one a month during winter, it is a rarity.

So I have two thoughts about this. First, is when you startup in the spring, if you are willing to experiment then before you lower your TA and add Borax see when your pool/spa is adding deposits again. Then, test your spa water when this occurs. Perhaps the aeration and high temps of the spa have raised its pH quite high. If that is true, then the things that waterbear suggested should help reduce the scaling problem. Of course, even if you test and things look normal, waterbear's advice is still good to slow down the pH rise and reduce your use of acid and should be tried anyway to see if it eliminates this scaling problem.

See above. doubt we've got a temperature issue worth mentioning. right now, spa and pool are a crisp 52F. However, it is true during summer that both pool and spa are in high 80s around clock.

My other thought is that perhaps this isn't scale but is something else. At first I thought it might just be evaporated salt, but this is a spillway and not splash-out on coping. Anyway, those are the random thoughts I had...at least you've got a good plan from waterbear that is sure to address some and probably all of the issues you are having.

Pretty darn certain it is scale. evaporated salt would come off tile much easier, and would likely do so with just scrubing and pool water. this stuff takes a fair amount of diluted acid (don't worry, I'm careful...did a lot of chem labs in college, so I know what the stuff can do if you are not careful). the scaling also occurs in a few other areas, notably a few nooks and crannies just above the water line where circulation isn't great. with my calcium getting higher...I just assumed it was scaling.

Richard

Thanks all