Some questions about water hardness

[Rszimm]

I'm in Tucson, which has some of the hardest water in the country. I built my pool almost exactly 3 years ago. It's a salt water system. The water desperately needs to be changed as the hardness level is about 1400. I've also got a whole lot of white fluff that gathers on the bottom of the pool and drifts around that I'm guessing is calcium precipitating out of the water.
Some facts about my pool: It's pebbletek finish and it has a lot of native rocks around the edges that are actually in the water (not just above or on the water lines). It's a cartridge based filter system. So here are my questions:

1. Is this white precipitate actually calcium?​

2. What's the maximum saturation level of calcium in pool water? I'm guessing it's around 1400 or else I wouldn't get the precipitate. I've also noticed that when the pH gets a bit high, I get a lot more, so I'm guessing it varies by pH (?).​

3. Why is my pool so hard already? I know people in town that don't change their pool water but once every 7 years or so and have never seen this precipitate. Is there something about a new pool that might cause a high calcium load right off the bat? Is there something about having native rocks **IN** the pool (and spillway) that's going to always cause me to have high calcium load?​

​

Just an aside: I'm currently building a rainwater catchment system that should get the water off my roof into a cistern and eventually into the pool. I'm hoping this will help me keep the water longer than 3 years. Water is EXPENSIVE in the desert...

 

[cowboycasey]

How are you testing the water? What is your CSI at now and when your PH goes up?

This will help us out to see what is happening.. Please fill out your signature so we can get a better picture of what you have

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www.troublefreepool.com

 

[JoyfulNoise]

Please answer Casey's questions above.

1. Is this white precipitate actually calcium?

It is very likely calcium carbonate. If you can, capture some of it using a turkey baster and paper towel. Let it dry indoors for a couple of hours. Put it in a clear glass or dixie cup and add a few drops of white vinegar. If it fizzes, it's calcium carbonate.

2. What's the maximum saturation level of calcium in pool water? I'm guessing it's around 1400 or else I wouldn't get the precipitate. I've also noticed that when the pH gets a bit high, I get a lot more, so I'm guessing it varies by pH (?).

You need to track your calcite saturation index (CSI). It is the combination of pH, CH, TA, temperature, and salinity that determines the CSI and whether or not calcium will scale in pool water. The pH inside your SWG when it is running is A LOT higher than in the main body of the pool water, so calcium scale will most likely form inside the cell. Maintaining CSI in a slightly negative range (0 to -0.3) helps reduce the chances of scale forming.

3. Why is my pool so hard already? I know people in town that don't change their pool water but once every 7 years or so and have never seen this precipitate. Is there something about a new pool that might cause a high calcium load right off the bat? Is there something about having native rocks **IN** the pool (and spillway) that's going to always cause me to have high calcium load?

Pan evaporation data for the Tucson area historically shows that the evaporation rate of water in a 1 year period is about 95-100" of water. That's basically your entire pool volume evaporating away. Your fill water has at least 180ppm CH in it. So your pool water will concentrate calcium over time. It is not unreasonable to see CH rise anywhere from 250-300ppm per year.

If you look in my signature there's a link to a thread for my whole house water softener. I had it connected to my autofill line. My pool now gets a steady fill of 0 CH water. Many people in Tucson have water softeners and, if they're smart, they connect them to their pool autofill or they manually fill the pool with softened water. Some people in Tucson are lucky enough to have well water (assuming you don't live near Davis-Monthan AFB where the ground water is contaminated) and many wells here have water that is much softer than the CAP water that the City of Tucson supplies.

Rain water is a nice solution but we only get around 10" of rain per year here. This year has been incredibly dry and we will likely fall well below the 10" average. Tucson is almost always in drought conditions every year. Given that, I wouldn't waste too much time trying to catch rain water and, if you do, use it to irrigate your plants. You need to find a way to use softened water to fill your pool or else you will be dumping the pool water every 2-3 years.

 

[Rszimm]

I'll go test full CSI this afternoon when I get a chance. I'm using the K-2006 for all my measurements (K-1766 for salt).

I have a bunch of that precipitate in my garbage can as I occasionally scoop up the piles with my net and dump them in there. I mixed about a teaspoon of the dried stuff with a bit of muratic acid and it fizzed like crazy.

The SWG is caking up bad enough that I'm currently cleaning it every month. I always wondered about using softened water in the pool. I suppose the added salt in the water is actually a benefit rather than a drawback given that I have a SWG, although I would imagine the salt would eventually build. Matt, how often are you doing a water change with Tucson Water with a softener? (I am also on Tucson Water even though I'm in the south part of Oro Valley).

I actually hooked my pool fill to my irrigation system. It's got four different supplies (Tucson Water, Fertilized Tucson Water, Softened Tucson water (plumbed but softener yet to be installed), and Rainwater (plumbed but also yet to be installed). There's a meter there that's monitored by the irrigation system and I'm able to select which supply to use for each "zone" and individually meter exactly how much each one uses, so I know down to the gallon how much water evaporated from the pool last year, and changing from rainwater to soft water to city water is as simple as making a different selection in the software.

I wonder if anyone has considered a softening system that raises pH significantly, allows the calcium to precipitate out, filter that, and then drops it back to normal.

 

[JoyfulNoise]

I'll go test full CSI this afternoon when I get a chance. I'm using the K-2006 for all my measurements (K-1766 for salt).

I have a bunch of that precipitate in my garbage can as I occasionally scoop up the piles with my net and dump them in there. I mixed about a teaspoon of the dried stuff with a bit of muratic acid and it fizzed like crazy.

The SWG is caking up bad enough that I'm currently cleaning it every month. I always wondered about using softened water in the pool. I suppose the added salt in the water is actually a benefit rather than a drawback given that I have a SWG, although I would imagine the salt would eventually build. Matt, how often are you doing a water change with Tucson Water with a softener? (I am also on Tucson Water even though I'm in the south part of Oro Valley).

I actually hooked my pool fill to my irrigation system. It's got four different supplies (Tucson Water, Fertilized Tucson Water, Softened Tucson water (plumbed but softener yet to be installed), and Rainwater (plumbed but also yet to be installed). There's a meter there that's monitored by the irrigation system and I'm able to select which supply to use for each "zone" and individually meter exactly how much each one uses, so I know down to the gallon how much water evaporated from the pool last year, and changing from rainwater to soft water to city water is as simple as making a different selection in the software.

I wonder if anyone has considered a softening system that raises pH significantly, allows the calcium to precipitate out, filter that, and then drops it back to normal.

No "salt" (sodium chloride) is added to the water when it is processed with an ion-exchange resin softener. The calcium and magnesium ions are exchanged with sodium ions but, other than that, no other changes occur to the water (chloride, pH, and alkalinity are unaffected). The only time a water softener uses brine (water saturated with sodium chloride) is when it is regenerating the resin bed and washing out all of the calcium and magnesium. After regeneration, the resin is rinsed several times so that there is no residue of the brine left.

My original pool water fill went from 250ppm to 1500ppm in just about 5 years. I then installed the water softener and I have drained and replaced several thousand gallons of water over the years to slowly bring the CH levels down. In a few weeks I will do another large water exchange. However, when I added the softener to the fill line, my CH stopped increasing. So, if my water had been within spec for CH, I would not have to do any water exchanges.

It sounds like you have both standard, potable city water and the irrigation only (non-potable) water from the purple colored water meter boxes. You should technically not use the "purple" water for anything but irrigation. It is reclaimed water (runoff and sewerage water) that is processed for discharge. It is technically clean enough to drink, believe it or not, but in order to have the "purple water" labelled as "potable", the City of Tucson water company would have to go through some very expensive regulatory certifications which they don't have the money to do. So the "purple water" is mainly used for irrigation purposes only.

In order to get softened city water, you will need to install a softener on the service loop and then have whatever plumbing setup you are using route softened water to your pool. You should never use softened water for irrigation - the increased sodicity from the extra sodium ions is bad for plants. Softener water can only be used for irrigation if you use potassium chloride in the softener instead of sodium chloride....however, potassium salt costs about $25 for a 40lb bag whereas sodium chloride costs about $6 for a 40lb bag.

 

[JoyfulNoise]

I wonder if anyone has considered a softening system that raises pH significantly, allows the calcium to precipitate out, filter that, and then drops it back to normal.

It’s called the Lime Softening process and it’s been around since the Roman times. However, the process of raising pH, precipitating calcium and then lowering pH increases the salinity of water by creating excess sodium chloride. Removing 500ppm of CH by the lime softening process can easily add around 800ppm of salt to the water. It’s a process that creates soft water but it comes at the cost of a lot of chemical steps and the need to further refine the water to remove the added salt. It’s not something that can easily be used for swimming pools.

 

[Rszimm]

It sounds like you have both standard, potable city water and the irrigation only (non-potable) water from the purple colored water meter boxes. You should technically not use the "purple" water for anything but irrigation. It is reclaimed water (runoff and sewerage water) that is processed for discharge. It is technically clean enough to drink, believe it or not, but in order to have the "purple water" labelled as "potable", the City of Tucson water company would have to go through some very expensive regulatory certifications which they don't have the money to do. So the "purple water" is mainly used for irrigation purposes only.

In order to get softened city water, you will need to install a softener on the service loop and then have whatever plumbing setup you are using route softened water to your pool. You should never use softened water for irrigation - the increased sodicity from the extra sodium ions is bad for plants. Softener water can only be used for irrigation if you use potassium chloride in the softener instead of sodium chloride....however, potassium salt costs about $25 for a 40lb bag whereas sodium chloride costs about $6 for a 40lb bag.

I may have misspoke. I only have a single service from Tucson Water. Just normal city water. I was only trying to describe how I've setup my irrigation/pool fill system. I know at some point I'll have softened water and rainwater, so I plumbed in everything a few years back in anticipation, even though I still have not installed the softener or the actual rainwater tank. Once I install a softener and rainwater tank, choosing between softened water, city water, fertilized water ( done with a MixRite Fertilizer injector) or rainwater should be just a flip of a software switch. That goes for any irrigation line or pool line.

I actually didn't know anyone got reclaimed water around here that wasn't a golf course.....

Incidentally, I just ran the numbers. I used 26097 gallons of water in the pool during the past 12 months (19640 in the past 6 months). That's way more than typical pan evaporation would imply. My guess is that our insanely long hot dry summer combined with the fact that I've got a spillway that runs when the pool is on is really killing me.

Oh, and I ran my CSI numbers and it seems I'm around 0.68. (although I'll admit there are a TON of different calculators out there on the Internet and they all seem to take slightly different inputs and yield slightly different results)

 

[JoyfulNoise]

Use the PoolMath App or the PoolMath calculator on this website to calculate CSI. Few other websites use CSI and some calculate only LSI.

You need to ensure your pool fill line is dedicated and not tapped off another irrigation zone. You don’t ever want to put “fertilized” water into a pool as that will cause a major algae bloom. You need to ensure your pool fill line does not contact water treated with fertilizer otherwise you’ll have to flush the line every time before using it to fill the pool.

 

[Rszimm]

Yep. That's the one I used. So does the 0.68 indicate that I'm 68% saturated? Precipitation would happen at a CSI of 1.0?

 

[JoyfulNoise]

Yep. That's the one I used. So does the 0.68 indicate that I'm 68% saturated? Precipitation would happen at a CSI of 1.0?

The scale is logarithmic based on the saturation of calcium carbonate in water. At a value of zero, the amount of calcium and carbonate ions dissolved in the water that can be absorbed or precipitated as solid calcium carbonate is equivalent to the saturation value of solid calcium carbonate in the water...in other words the water is holding the exact amount of calcium and carbonate ions in solution that is can possibly hold. When the value is positive, that means the water is over-saturated with calcium and carbonate ions and scaling is likely. When the value is negative, that means the water is undersaturated with calcium and carbonate ions and it is aggressive towards plaster. A value of +0.3 means that the water is currently hold about twice as much calcium in solution that it is able to hold based on the thermochemistry. At a value of +0.6, your water is holding a little under four times as much calcium as is possible. These values represent a thermodynamic driving force for either etching or scaling but they say nothing about the rate (thermodynamics and chemical kinetics are two different aspects of a chemical reaction...just because a chemical reaction CAN occur does not imply that it WILL occur).

With such a highly positive CSI value, your water has a huge driving force to want to scale calcium out of solution. That is definitely happening inside your SWG cell and it is likely happening in your natural rock spillway. You may see a "bathtub ring" of calcium scale on your waterline tiles. You need to replace water as the CH is just too high. You also likely need to lower your pH and TA and monitor those values more closely. pH and TA are your biggest "levers" for adjusting CSI. CH is a lot harder to control because reducing it can only be done with water exchange.

 

[Rszimm]

Thanks for all your help Matt. I'm not sure if this is allowed on the forum, but would you care to share the make/model of your softener? Are you happy with it? I figure the loop is there just waiting for me to install it and it would seem like a good opportunity now that I'll be draining the pool soon. My loop is outside on the south side of the house. I've heard people who technically should know what they're talking about recommend anything from "it'll be totally fine...they're designed to be outdoors" to "you'll have to build a sun-tite enclosure around it" to "bury the tank in the ground to protect it from the sun". I'm still debating about what to do.

 

[JoyfulNoise]

WaterTec is the local manufacturer/installer I went with. I have their Eliminator Plus whole-house system (mineral removal and chlorine/chloramine removal).




You’ll have to work with their technical sales people to figure out what to do for an outdoor system. I know they do make systems rated for outdoor use but it may require some special enclosure. Sun and heat destroys everything here but you also have to worry about overnight freezes that can cause pipes to burst. I’m actually quite surprised the home builder put your service loop outside your house, plumbers almost always set them indoors in the garage. Perhaps there’s a way to redo the plumbing for that.