Controlling Calcium - Adding NAC Filter

JoyfulNoise said:

First off, I have no idea what a NAC is but it sounds like a bunch of the usual water pseudoscience nonsense. There are a lot of products on the market that make very ridiculous claims about what they can do and 99.9% of it is garbage. Just enough science to sound fancy and just enough wiggle room so that their claims hold no liability to them. So before we talk about NAC, you better post up some REAL peer-reviewed scientific data about them. Otherwise, it’s pure marketing BS.

As for living in Tucson and pools - get a standard whole house water softener based on salt regeneration and ion exchange resins (you know, the technology that’s been around forever and actually works) and run a like out to your pool autofill or just create an outdoor spigot. Then used softened water to do top offs. When you do that, your CH will stop rising. If you need to lower CH, draining the pool and refilling with standard city water (~ 200ppm CH) is fine.

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(P.S. - I have a PebbleTec pool with a concrete base. I'm not sure why that's not listed as a pool choice unless it's just lumped in with "Plaster," which doesn't make any sense to me.)

Much thanks. The six whole house filters we have including the NAC filter work fantastic. It's not pseudoscience - - it's a well known water filter technology that has been used for years for softening water but more importantly, removing or neutralizing many water contaminants. A big difference from just a ion water softner system that only conditions and changes the hardness level. A whole house water filter system is generally a better choice than an ion-exchange system, especially if you need to remove a wider range of contaminants. Ion exchange systems, primarily known for water softening, may not address all water quality concerns. A complete water filter system, on the other hand, can remove a variety of impurities, including Volatile Organic Compounds (VOCs), PFAS, pharmaceuticals, arsenic, chromium-6, and more. No calcium deposits on our shower heads and much better for appliances. Great tasting water and my wife has many aquariums and it's much easier with her water changes. We replace our filters every nine to twelve months. Ion exchange is great for softening water but not as good for removing contaminants. With a six stage filter - - we have that covered pretty well. (See attached pic)

***But thanks for your idea about topping off the pool with softer water. I've decided to go a step further and I'm going to add one, single, dedicated (separate) NAC filter directly to the water line to our pool. Just one filter will remove significant calcium (not all, though) and that sounds like a solution that I can optimize CH levels within the recommended 200-400ppm range. Especially with extremely hard water in Tucson and even more (based on Tucson Water Reports) in our specific location.


(Filter system - 2 sediment, 3 carbon, 1 NAC)

Okay. You have all convinced me. No NAC filter. I’ve been able to maintain the water nice and pristine but the light calcium ring that I brush off reappears after awhile. A major PITA. I had the pool tiles professionally cleaned this late March, 2025, and replaced around 2,000 gallons from a local fresh water source. Compared to what it was, it’s far better. I guess there’s no getting around the hardness of the water and the calcium content here in Arizona. It seems like any cure is worse than the disease. At least I’m not boosting the CYA level by using just liquid chlorine as opposed to the pool company’s stabilized tabs. Plus - factoring in the CYA level for the right CL ppm. Thanks to everyone for responding. It is greatly appreciated.

JoyfulNoise said:

I prefer ion exchange systems for actual mineral hardness removal (mine also has a secondary GAC bed to remove chlorine/chloramine/heavy metals). Then I use 5-stage point-of-use filters on drinking water areas (kitchen sink and refrigerator). PoU's could either be RO filters or simple carbon block/GAC filters. I prefer RO water for drinking.

NAC is all well and good but the data on it is sketchy at best. These types of warning are common with NAC literature-



So, as @mknauss stated above, in a pool top off situation, a NAC filter would be useless as any crystallized minerals would redissolve as they sat in the pool volume.

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Much thanks.

mknauss said:

Pebble Tec is a plaster pool. The material holding the pebbles together is plaster.

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Thanks. It sure looks and feels far different than any plaster pool I have been in. The greatest percentage of the base is stone (pebbles) correct? So the small amount of plaster used to adhere the pebbles (not cement?) is plaster therefore it’s classified as a plaster pool? They use plaster as sort of a grout for the bottom of the pool? Still confusing to me.

Pebble Tec® is made up primarily of small pebbles, white portland cement, and coloring. What makes this product unique are the pebbles themselves. These pebbles are harvested from around the world for their color, size, and smooth shape and are combined to create a wide range of colors. Typically 90% of the finish exposed to the water is stone that is not affected by the waters chemistry, leaving only 10% (cement) that can be affected by the water. Standard plaster finishes by contrast have 100% of their finish affected by water chemistry. This translates into a more durable surface that is more forgiving of the pools water chemistry.

mc2021 said:

Are you able to run the calcium test on city water vs after your filters?

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I’m going to do this tomorrow. I thought about it before but even with lower calcium, what I’m being told about the NAC process is that it’s fine for a closed environment like running your household taps and showers. But once in an open environment like a pool, the crystals will go back to their original state, which I assume means it turns back to calcium and whatever was crystallized/neutralized? Thx.

Newdude said:

Or worse. The 'unstabilized tabs' that they switch to when the CYA gets jacked. They are cal-hypo.



Exactly like that.

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O.K. - it is what it is. The composition is

Newdude said:

Or worse. The 'unstabilized tabs' that they switch to when the CYA gets jacked. They are cal-hypo.



Exactly like that.

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Well, I guess it is what it is but it isn't a plaster pool to me. Not with the stone base percentage and how different it is from a plaster pool. What, 2% plaster and it's a plaster pool? I look on the bottom of my pool and see nothing but stone and cement. And I sure feel the difference, too! (Not that it bothers me as I prefer the Pebble Tec look and cleaner bottom.)

There are vast differences between a Pebble Tec Pool and a Plaster Pool. Who makes these rules? This definition? Ah, it's just one of those "Let It Be" deals. Got it.

One final comment. If I understand correctly, there is NO way to completely and SOLELY remove Calcium from water without removing other minerals. Correct? Which means that you could end up with softer water and a lower pH that you would have to adjust. Even with a reverse osmosis water system - - I believe it removes other vital minerals that would be beneficial for you pool. Is this assumption correct?

Newdude said:

Forget the brochure mumbo jumbo or personal preferences here. Some people do waterline tiles on their fiberglass pools and have to follow plaster recommendations because of the grout. You're at least following it because the grout is plaster if that helps.

But from a chemistry standpoint, if there is any plaster or grout, plaster guidelines are followed for the same reasons.

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Will this be on the mid-term exam?

mknauss said:

From my reading, the NAC or TAC only changes the 'character' of the mineral, does not remove it. Thus, in a pool, as it is a closed system, those minerals (calcium) will continue to build up. And cause scaling.

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Let me see if I've got this right. With TAC or NAC, once crystallized, they’re no longer able to stick to pipes or fixtures. TAC or NAC systems (Template-Assisted Crystallization/Nucleation Assisted Crystallization) are often called “salt-free water softeners,” but technically, they don’t soften water. Instead of removing minerals, they change the structure so minerals won’t stick and form limescale. It’s a big win for your plumbing — but doesn’t meet the strict definition of softening. (But good enough in some instances to notice a softening difference.)

I believe you are saying that TAC & NAC (interchangeable) change the structure so minerals won't stick and form limescale (in what I would call a closed system in that you would drink the water or have it pass through your shower head and appliances (refrigerator/washer/dryer/dishwasher) but a closed pipe system that is being flushed out and NOT in a pool of water, exposed to the sun & elements, in which you are saying that whatever crystallization that takes place reverts to its orginal state? Be that calcium or any other mineral that has its mineral structure changed?