Minimum Calcium Needed

[Pro Golfer Mark]

Just some background, I have an 18 month old plaster pool in Las Vegas where we have hard water. I'm getting the PuriPool process done on my pool soon because I'm tired of looking at the stains on my tiles. My CH is currently at 700. Now I'm assuming the puripool process is going to set me back to zero or at least low enough on calcium where I'm going to have to add some back. I'm thinking that I want to set it as low as possible because my autofill is just going start adding back calcium on day one and I'd like the keep the levels low for as long as possible. Is it realistic to think that R/O is going to remove that much calcium, and if so what level should I target when adding back the calcium?

 

[kimkats]

Pool School - Recommended Levels

I hope this link helps.

I don't know if R/O will remove calcium. I know it is used to remove CYA.

Kim

 

[Patrick_B]

The RO will remove everything from the water thst is a dissolved solid. Calcium, Cya, alkalinity, salt, etc. how far they take it all down depends on the RO unit, and how long they process the the water through it. You are correct, your tap will just add it right back in, but you have to have some, or the water will be corrosive to your finish. If it was my pool, I wouldn't start below 150-200 CH depending on what my fill water TA and pH were. High levels of CH can be managed with diligence, and I know, because I am managing 800+ now, and others have done similar and more. One I know of here is Richard320.

The unfortunate truth, is that most people have some CH to contend with, some, like us a whole lot.

 

[JoyfulNoise]

As an aside to the mods and experts here, check out the PuriPool website, they copy the FC/CYA chart exactly and they have a "PoolSchool" as well. Maybe a TFPer owns the company??

My water is currently at 750ppm CH. It is crystal clear and I get no calcium scaling anywhere (I have a blue tile at the water line so I would know right away if I get scale).

You can manage high CH, it just takes careful monitoring of the CSI and keeping your TA and pH down.



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[Ale_Brewer]

JoyfulNoise is right. You can spend a lot of money and eliminate the calcium but it's only temporary. It's much easier and cheaper to just balance it out to avoid scaling. It's all about temporary hardness and permanent hardness. When the TA exceeds the CH all hardness is temporary, which means no scaling. When the TA is less than CH, both permanent and temporary hardness are present. Permanent hardness will produce scale. pH also has an effect on this, but generally speaking TA-CH=TH or CH-TA=PH

 

[JoyfulNoise]

JoyfulNoise is right. You can spend a lot of money and eliminate the calcium but it's only temporary. It's much easier and cheaper to just balance it out to avoid scaling. It's all about temporary hardness and permanent hardness. When the TA exceeds the CH all hardness is temporary, which means no scaling. When the TA is less than CH, both permanent and temporary hardness are present. Permanent hardness will produce scale. pH also has an effect on this, but generally speaking TA-CH=TH or CH-TA=PH

Hi @Ale_Brewer

TFP doesn't really use the terminology "permanent hardness" or "temporary hardness" (I believe those are used in the water treatment industry). It gets too confusing. The most relevant parameters for pool water vis-a-vis calcium scaling are total alkalinity (which is mostly dominated by bicarbonate alkalinity), calcium hardness (directly measured by the Recommended Test Kits) and pH. The nice part about using the PoolMath webpage is that it takes into account all of the measurements that TFP'ers normally make and then calculates the Calcite Saturation Index (CSI) which is extremely useful for predicting the potential of your pool water to either want to deposit calcium or absorb calcium if a calcite source (e.g., plaster) is present. The CSI is logarithmic and pool water should be maintained between -0.3 to +0.3 on the CSI scale. Beyond -0.6 or +0.6, and you are in danger of either plaster damage via etching (negative) or calcium scale (positive).

So even though my water has 750ppm of calcium in it, I do not get scale because I try to keep my water's CSI between 0 and -0.2 at all times. I was able to do this by first lowering my total alkalinity to <70ppm, adding 50ppm borates for additional pH buffering and maintaining a pH lower then 7.8 (typically not lower than 7.5 unless I'm reducing TA). In my first winter with the pool (it's open all year round), I got lazy and did not keep my water properly pH balanced and I developed horrible, thick and rough calcium scale along the entire water line of the pool and the spa tile facade. That mistake cost me $300 to have a professional come and soda-blast off all the scale. So now I maintain a proper CSI and I have not had any scale since (and my CH was lower than it is now during that winter when I let the scale form). The only problem I have with calcium comes from evaporite deposits (hazy white films and salt formation) which is very easy to remove with a dilute acid spray.

So, for anyone with high CH, maintaining a scale free pool is possible and PoolMath makes it very easy to calculate what you need to do to get your pool water properly balanced. That said, there is a place eventually for either RO treatment or draining and refill (depending on cost) because once the CH gets too high (say above 1200ppm), you really can't realistically adjust other water parameters (like pH and TA) to compensate. It would mean maintaining an unadvisedly low pH or TA which could then damage other pool equipment such as heater cores or metal hand rails. So there are limits, but with judicious use of low CH water sources (like using rain water collection systems), it is possible to extend the timeframe between water replacements greatly.

 

[JesseWV]

You can see "BBB" mentioned in several of their PoolSchool articles so it seems like they have copied articles directly from TFP in the past. They even have a link to the old PoolCalculator.com there.

Edit: Upon looking more, it looks like they've "borrowed" quite a bit, almost the entire Pool School section, and edited it to suit their needs.

As an aside to the mods and experts here, check out the PuriPool website, they copy the FC/CYA chart exactly and they have a "PoolSchool" as well. Maybe a TFPer owns the company??

 

[duraleigh]

Puripool guys, Bruce and Sal, were around here for a couple of years. What they wanted was free advertising and Jason Lion and I must've spent several hours on the phone with them trying to get them to conform to forum rules but they simply couldn't do it. They just kept pushing their products.

They eventually got banned and set up a "We'll get even" website that was a carbon copy of TFP....I think it managed 40-50 posts....almost all made by themselves.

I have no idea if their r/o is successful but I wish them no luck. I do not believe them to be honest business people.

 

[Ale_Brewer]

I guess I should disclose that I work in industrial water treatment.

 

[chem geek]

JoyfulNoise is right. You can spend a lot of money and eliminate the calcium but it's only temporary. It's much easier and cheaper to just balance it out to avoid scaling. It's all about temporary hardness and permanent hardness. When the TA exceeds the CH all hardness is temporary, which means no scaling. When the TA is less than CH, both permanent and temporary hardness are present. Permanent hardness will produce scale. pH also has an effect on this, but generally speaking TA-CH=TH or CH-TA=PH

Temporary hardness is defined as the hardness that is removed (through precipitation of calcium and magnesium carbonate) after boiling the water while permanent hardness is that which remains soluble after boiling (as calcium chloride, calcium sulfate, calcium nitrate, etc. -- see this link and this link). In practice in pools, most of the initial hardness from fill water is "temporary" in that it is from calcium and carbonate and not from other salts such as chloride and sulfate (i.e. we usually find that high CH fill water also has high TA) while the hardness added from calcium chloride product is permanent. It is not true that when TA exceeds the CH that there will be no scaling nor is it true that the "temporary" hardness does not produce scale. One can absolutely positively get scale by raising the TA too high even if the CH isn't particularly high. This can most easily happen in hot tubs because the water temperature is higher and we've seen scaling there if the TA is not lowered or the pH gets too high.

Again, "temporary" hardness absolutely positively can produce scale. What is "temporary" is that the hardness (calcium and magnesium) can be precipitated by boiling so is no longer measured as hardness in the water that remains. IF you do this in a tea kettle, the calcium carbonate can coat the metal of the kettle (i.e. scale).

One way to prevent scaling is to ensure that the Calcite Saturation Index (CSI) is not greater than 0 though in practice we don't normally see scale actually form until the CSI gets to around +0.7 or so in pools though in hot spas it can be seen at around +0.3 or so. The CSI does not determine the rate of scale formation; only whether it is thermodynamically possible. Likewise, a negative CSI says whether it is possible for solid calcium carbonate to dissolve into water (i.e. whether plaster can dissolve), not the rate at which it dissolves. The rate appears to be more related to the pH where the rate is higher/faster at lower pH (at least for dissolving when the CSI is negative and speculatively for scaling as well when the CSI is positive).

The reason that CSI is the best scale predictor for pools is that calcium carbonate is generally the first solid to precipitate out of the water because it is the least soluble at normal CH, TA, pH and temperature in pools. Magnesium carbonate is much more soluble and we have never seen a pool that had enough magnesium to precipitate magnesium carbonate. Very rarely there are pools with very high calcium and very high sulfate that have precipitated calcium sulfate (see The Mystery of the Pointed Crystals, Large Crystals in My Pool, and Sediments/Crystals on Pool Bottom). So these are examples of "permanent" hardness being able to produce a different kind of scale (calcium sulfate, in this case).

There is a lot of incorrect science on several websites such as this one that pretends that there is this chemical called calcium hydrogencarbonate, Ca(HCO₃)₂, when in fact almost all of the calcium (Ca²⁺) and bicarbonate (HCO₃^-) in the water are separate ions. There is a small amount of various calcium ion pairs, but they normally represent less than 3% of total calcium. These sites show that boiling water creates calcium carbonate via creation of carbon dioxide, but what is really going on is that there is already carbon dioxide in the water because it is over-carbonated and boiling the water drives it out faster which raises the pH thereby increasing the carbonate concentration. The higher temperature also precipitates more calcium carbonate because it is less soluble at higher temperatures. The following shows the CH and TA combinations that saturate the water with calcium carbonate (CSI is 0) at 212ºF and at a pH where carbon dioxide outgassing has stopped (is in equilibrium with the air). You can see that such saturation has nothing to do with whether CH is larger or smaller than TA and obviously one could have both CH and TA be very high and would clearly scale even if TA > CH so long as the pH were not very low. To imply that 500 ppm TA with 200 ppm CH or that 400 ppm TA with 300 ppm CH won't scale at a pH of 8.0 is ludicrous.

CH .... TA .... pH
. 25 ... 49 ... 7.95
. 50 ... 35 ... 7.8
100 ... 26.5 . 7.65
200 ... 21 .... 7.52

I don't see the usefulness of distinguishing between temporary and permanent scale or comparing CH vs. TA as this has nothing to do with actually predicting the potential for scaling. Calcium carbonate scale can occur when the product of concentrations of calcium ions and carbonate ions exceeds the solubility product of calcium carbonate and it cannot occur when such product of concentrations is less than the solubility product.

 

[chem geek]

I'm thinking that I want to set it as low as possible because my autofill is just going start adding back calcium on day one and I'd like the keep the levels low for as long as possible.

You don't want to go too low in CH or else you can potentially dissolve the calcium carbonate from your plaster pool surface. It should be fine to shoot for a somewhat negative CSI (from low CH) since this will be temporary and the CH will rise over time. If you shoot for -0.3 in CSI then going from that to +0.3 over time from CH rise is a factor of 4 in CH. So that should give you reasonable "room to grow" in CH.

 

[Pro Golfer Mark]

Thanks everyone for chiming in and helping out. I had the PuriPool process done on Friday and wanted to report back. It turns out the process didn’t remove all the calcium after all, but did bring it down significantly. First here are the numbers from my TF100 test kit:

Before:
FC: 6
CH: 1,000 (The PuriPool guy measured it at 1500 on his test)
PH: 7.6
TA: 45
CYA: 35
Borates: 0
TDS: 4000+ (I didn’t measure this as I don’t have the test , he said it was so high, it was off the charts)

After:
FC: 0 (He neutralized my chlorine with sodium metabisulfite before the process)
CH: 175
PH: 7.5
TA: 45
CYA: 0 (or at least undetectable, the test solution is clear and I can see the spot on the bottom of the tube even after filling it up completely)
Borates: 0
TDS: 300

Derek from Clarity pool service showed up around 6:30am to set up. He was a super nice guy and seemed very knowledgeable about pool chemistry. I told him about TroubleFreePool and how I follow the methods here and he knew about the site and said it was good. After getting set up he tested the water. He was shocked by the high TDS in my pool. He had never seen levels that high before. I guess he has never had a customer that only uses liquid chlorine. I’ve been using liquid chlorine exclusively since my pool was built in fall of 2013. After telling him how I use half a gallon a day during the summer months, he said that would explain it. It was all the salt from the chlorine. Of course, we here all know TDS really doesn’t matter.

He started his pumps around 7:30 and they ran until around 4pm. I have an 8000 gallon pool with a 1500 gallon spa. He only filtered the water in the pool and his flow meter showed that he pumped through 10,000 gallons. He said he let it go a little overtime to get the water extra clean because we would be adding back the untouched spa water. The “after” numbers above are after the pump running for three hours mixing the spa water back in.

It may be placebo, but my water seems clearer and feels better. Mentally, it just feels good to know that I have some of the most clean pool water in town. I don’t have to “manage” any high calcium levels, because I don’t have them. I think the process was worth the money and I recommend it.

I added a gallon of chlorine soon after the process to bring the FC level up. I’ve been using trichlor tablets instead of liquid chlorine for the past couple of days at Derek’s recommendation. He said this was the most cost effective and easiest way to bring my CYA back up. I have to agree. I don’t have the expense of chlorine, muriatic acid, or CYA. No daily visits to the pool adding chemicals, I can just let the floater add everything for me. I figure I’ll just let the tablets do the work, check my CYA every few days, and then go back to liquid chlorine and acid when my CYA reaches 40. What do you guys think about this? How many trichlor tablets should it take to bring my CYA is back to that level?

Also, my TA is below the recommended level of 70. What do you think I should bring it back up to?

I think I’d like to roll with my 175 CH for now. I tested my fill water and it has a CH of 375. With the Vegas heat, I’m sure my autofill has been adding back quite a bit.

 

[YippeeSkippy]

Can you share with us how much the treatment cost? If you don't mind, of course! I'd love to see more R/O available.

 

[Patrick_B]

Their branch in DFW wanted 1200-1400, estimating 200-300 for travel fees. This would be taking my 27500 or so gallons from 780 CH to less than two hundred.

 

[JoyfulNoise]

I would suggest you be very careful to keep an eye on your TA and pH while using trichlor tablets. They are very acidic and will reduce your TA since you're using them to replenish CYA. For every 10ppm FC added by the trichlor you'll get 6ppm of CYA and a decrease in TA of 7ppm. If your TA crashes while adding the trichlor, your pH will drop drastically and swing around wildly.

My suggestion would be to add a little baking soda to get your TA up to 50-60ppm and then add the trichlor while monitoring the TA and pH. Your fill water may also add some TA as well but that could be too slow relative to the rate of destruction by the trichlor.

Also, with your CH so low, your CSI is now around -0.38. I'd would let your pH drift up to 7.6 and not let it go lower than that so that your CSI stays in a reasonable range.




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[ping]

If your are planning on using pucks for a while then raise the TA to 100 for the time being. Once you start using bleach then you can play with a lower TA to keep the pH from rising too fast.

 

[JoyfulNoise]

Their branch in DFW wanted 1200-1400, estimating 200-300 for travel fees. This would be taking my 27500 or so gallons from 780 CH to less than two hundred.

Wow!!

I'd like to know the cost as well if the OP is willing to share plus how much water was rejected to waste. Typically you get 85% water RO'd and 15% sent to waste. Did you have to add back with your garden hose?

 

[Patrick_B]

I didn't do it, and not sure if I will for another season or two. Likely, I'll truck in the reject replacement portion, but I couldn't nail them down on the amount because of the unknown SDI. Which I understand, but I told them I could do one when the time came. I fear with my high numbers, I'll be extremely lucky to get a 15% R.R.

 

[JoyfulNoise]

I didn't do it, and not sure if I will for another season or two. Likely, I'll truck in the reject replacement portion, but I couldn't nail them down on the amount because of the unknown SDI. Which I understand, but I told them I could do one when the time came. I fear with my high numbers, I'll be extremely lucky to get a 15% R.R.

Got it.

I'm at 750ppm CH and I'm hoping I can finish this season and get one more swim season in before having to consider it. I'm also keenly interested in rainwater collection cisterns as hundreds of gallons of water rolls off my roof with every down pour and it all just washes away. I'd love to collect and use it. But that's a post for a different day.


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[Pro Golfer Mark]

The cost was $525.

I'm not sure how much water went to waste. I do know that he hooked up a garden hose from my house to the trailer to replenish water. He also had a hose from his trailer to my sewer clean out to dump the waste. The water in the pool dropped by 1 to 1.5 inches during the process, but never below the tile line. My autofill took care of the rest after he was done.