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Lowering The Calcium Hardness (Ch)

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I live in an area with fairly hard tap water - 260ppm - and I have neither a decalcifier nor a well with soft water. Therefore I don't have the option of changing part of the water in order to lower the CH.

I was targeting 130ppm and the local spa dealer sold me a liquid "hardness stabilizer", consisting of a "mixture of carboxylates".

Adding about 25ml to my 1600l spa brought me down to 200ppm. Gradually adding up to 100ml more in steps of 20ml had no effect at all. The CH remains on a plateau of 200ppm.

Looking through the old posts I only found one possibly fitting reference to carboxylates:

There are other factors as well such as the combination of hard water (CH) with soap. This forms scale (soap scum) with calcium while the TA has very little to do with this. The soap scum is not calcium carbonate, but a precipitate of calcium attached to (usually) two soap molecules (fatty acid salts with a water hating long end and a water loving carboxylic acid group and it is that group that attaches to the calcium forcing the molecule to precipitate out of the water). As you point out, people bring things into the spa and the relatively low water volume per bather means that it doesn't take much to throw things out of whack. Though I agree that the body soaking in a spa can change the pH, I think it is important to quantify that before assuming that a TA of 60 is inadequate, for example.

I am going out on a limb in suspecting that part of what is causing the high CH has been felled by the carboxylates and is probably now residing in the filter, but another part is still in solution and is not being touched by them?

I guess 200ppm CH is acceptable, but I'd still like to understand what's going on...

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Polycarboxylates are a weak form of metal sequestrant that mostly operate by disrupting crystal formation during the initial stages of creating calcium carbonate scale. So that's why it doesn't lower the measured CH reading by very much, but it will inhibit scale formation in spite of the higher CH reading. I think that using an HEDP-based metal sequestrant at somewhat higher concentrations (though still in the 1-10 mg/L range) would be even more effective for that purpose, but you might not need to do anything at all if you instead just get your TA much lower down to around 50 or so. It depends on the method of sanitation you will be using and the typical resulting pH. If it tends to keep the pH lower, then I don't think you have a problem.

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Thanks chem geek, I think I understand now. :-)

It depends on the method of sanitation you will be using and the typical resulting pH.

I was planning to continue using bleach/dichlor. Changing to another method is not entirely out of the question if need be, but I'd probably try with another sequestrant first.

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OK, yes with Dichlor-then-bleach you'll probably want the CH lower just for safety since the pH will tend to go up. If you use an HEDP or other metal sequestrant that says it binds to calcium, let us know. Another technique for lowering CH is to add sodium oxalate (or oxalic acid, but that lowers the pH significantly) to form calcium oxalate precipitate, but you'll need to be able to vacuum that out (see this post) or otherwise get it to the filter to remove (or try using it with fill water outside the spa, separate the precipitate from the water, add chlorine to get rid of the oxalate, then add to the low CH water to the spa). Or you can use sodium citrate (or citric acid, again that lowers the pH) to form calcium citrate. I think the oxalate is the better approach because when you add chlorine the oxalate gets oxidized to carbon dioxide whereas with citrate you form chloroform as a by-product. Or you can use HotSpring® Vanishing Act™ Calcium Remover which sounds like the easiest way, though probably not cheap (it lists for about $40).

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HEDP seems to stand for a number of things. I expect you mean 1-hydroxyethan-1 C2H8O7P2 or CH3C(OH)(PO3H2)2 . This seems somewhat hard to come by at a reasonable price, unless what I need is like a really miniscule amount per water change. We're talking about 30EUR plus shipping for 2g at 96% purity! [EDIT] At your suggested 1 to 10mg/l I'm looking at 1.6 to 16g per water change, so I'll be somewhere between 30 and 250EUR. This is not promising. [/EDIT]

By what I can see looking at the Vanishing Act Calcium Remover, I am suspecting it could be simply a bag containing a molecular sieve, such as Zeolith A, which is readily available here and really cheap. The only drawback I see is that I will have to vaccuum it out afterwards if I can't contain it in some kind of bag like the one Vanishing Act comes in. As it's a hot tub, I wasn't planning on getting a vacuum...

http://www.ultrachem.in/zeolite-a.htm mentions an average grain size of 4microns. Don't know whether that's just manufacturer-specific. I'm considering obtaining a 1micron filter bag like the ones at http://www.filterker...lterbeutel.html and simply hanging a scoop of Zeolith A in the skimmer/filter intake. Do you think this is worth trying?

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I don't know what they use in Vanishing Act so I can't really comment whether your Zeolith will do any good, but unless it's some sort of ion exchange resin, a simple filter sieve isn't going to do it -- calcium ions are exceptionally small (even polymers slip through most filters).

As for the HEDP, it's fairly common in some metal sequestrant products. In the U.S., it's available in products such as ProTeam Metal Magic and Jack's The Pink Stuff that are not nearly as expensive as you describe. HEDP is 1-hydroxy Ethylidene-1,1-diphosphonic Acid C2H8O7P2 as you described.

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Zeolith A is so cheap since it's so widely used as a water softener in washing machine detergents. If I understand correctly, for this application it inclucedes natrium ions which are exchanged for the calcium ions, so it seems to be set up to work just like a resin with the main difference being that resins are usually regenerated for multiple use and this stuff is usually used only once.

So I've obtained some from a source for diy modular detergent components and I'm almost ready with my filtering setup, so I'll be able to report in a couple of days.

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It's sodium that is exchanged for the calcium (two sodium for one calcium). Zeolite 4A is a form of sodium aluminum silicate used in detergents. That may very well be what is used in Vanishing Act. Anyway, if you are able to use this stuff and not make a mess (i.e. have it stay self-contained), let us know. Also let us know where you buy it. This could be a great inexpensive way of reducing calcium in spas. I'd also like to calculate what it would take to lower the CH in pools filled with very hard water, but I suspect it may become cost prohibitive in that situation.

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I'm just wondering if there have been any changes to this advice in the last few months.

In fresh water my CH is about 275. Just under 3 months in on the current fill, my CH is about 450. As water evaporates and I replace it, the CH just gets worse. I live in a desert in the middle of a drought, so I'd rather deal with the CH than dump the water more frequently.

I've asked other places and been told there's a water filter that attaches to a garden hose. I found those on Amazon, but they talk about filtering out Chlorine and such, with no mention of calcium. That could be me not understanding what I'm reading though. http://www.amazon.com/BMS-Garden-Hose-Filter-Single/dp/B004NWZP7Y/ref=sr_1_3?s=lawn-garden&ie=UTF8&qid=1362729143&sr=1-3&keywords=water+softener

I looked at the Vanishing Act Calcium remover bags, but they look to be about $35 a piece and say "Multiple calcium removers maybe needed if initial water hardness is above 200 ppm" which makes me think that could get expensive fast.

Any new suggestions?

Edit: And just after I posted I found http://www.poolproducts4less.com/united-chemicals-calcium-hardness-reducer-caltreat.html

Thoughts?

Edited by deld

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See the following and use a water softening cartridge:

http://www.purewaterproducts.com/gardenhosefilters.htm

http://www.purewaterproducts.com/products/fc024

http://www.purewaterproducts.com/docs/howto-regenerate-softening-cartridge

And yes, CalTreat is another approach where it essentially precipitates calcium so that it can get caught in the filter, though may result in some loss of water clarity.

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This is great! Thank you!

I'm thinking I might try the CalTreat on this fill, and get a filter for the next one.

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Ok, zeolite was an interesting idea, but it's not practical for this application.

It comes almost in powder form and the sieves that are available at acceptable prices are just not fine enough to contain it. Bottom line: You can't filter water though zeolith without bringing at least some of the zeolith into the water and therefore the pool. Thankfully the stuff sticks together and deposits at the water line, so I was able to get it out within a week or so and didn't have to change the water. In its normal use in washing detergents this is irrelevant as it is drained together with the water it softens.

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Now I've found something that works: I've obtained by online auction for somewhere around 50€ a water softener normally used with professional Italian coffee makers: The DVA LT8. The pictures show it after I fitted a couple of German standard garden hose quick connectors to it.

DVA-LT8_PICT0001a.jpgDVA-LT8_PICT0002a.jpg

According to the specs it softens 900l of 22°dH (400ppm CaCO3) water before it has to be regenerated using 1kg of salt. The water here is said to have 20°dH (I measured by multiple titration 260ppm CH as mentioned in the first post above).

I estimated that I would be able to fill my 1600l tub in one go (without regeneration) and come out around 100-130ppm. As I didn't quite trust that estimate, I regenerated once at half fill. I had to add 100g of calcium chloride dihydrate to bring it back up to 120-130ppm CH from the resulting 60ppm CH. Next time I will go by my original estimate... :-)

One thing I'm not quite sure about is what do I do with the water softener while it is not in use. I will only need it every couple of months, when I refill the tub. During the interim there is always a residual amount of water in it, keeping the resin wet and therefore the whole container humid. Is this harmful? Will I have to decontaminate it before use? Will a regeneration cycle with that 1kg of NaCl provide sufficient decontamination? Or will I have to make an effort to take out and dry the resin before storage?

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deld,

have you tried the CalTreat?

use a water softening cartridge:


http://www.purewaterproducts.com/products/fc024

These cartridges are 2.5" (6.35cm) x 9.75" (24.765cm), giving a max. volume of about 3l of resin if filled to the brim. My LT8 contains about 27l of resin, if I calculated correctly. So If I was going to fill my 1600l (423gal) tub using 260ppm CH tapwater aiming for 130ppm CH, I would expect to go through somewhere around 9 cartridges (or regenerations) for a fill. Your water is even harder than mine, so you might expect to go through 10 on a same size tub.

10 cartridges cost 190$ (or alternatively 9 overnight regeneration cycles, which means it would take you well over a week to fill the tub using one cartridge).

So you might want to look for a larger filter.

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A trove of good comments, thank you all! 

Chem Geek mentioned Zeolite4A. I found it in an inexpensive pellet form on Amazon that can be heated and reused. I'm a newbie so may be missing something but it seems like an affordable option for a hot tub:

Molecular Sieve Zeolite 4A 8X12m 300g

https://www.amazon.com/gp/product/B01MDSU1KT/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A1MWRZVF3AZEJX

4A molecular sieves are the sodium form of aluminosilicate zeolite A. Their structure forms a network of pores approximately 4 angstroms in diameter, through which only very small molecules such as water, methanol and hydrocarbons up to propylene can pass. This makes them useful for removing water from mixtures with larger molecules. They can absorb up to 20% of their weight of water, depending on the surrounding water concentration and other conditions. They can be dried for reuse by heating at 200-300C (400-600F).

 

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