Metal Trap vs RV Water Softener for top-ups

[GaryParr]

Its a 19k gallon vinyl liner salt water pool and I'm on well water. I'm about to go through an AA treatment (polyquat, Jack's purple stuff, and AA already ordered) due to some wonderful brown staining. My understanding is that my DE filter should trap the sequestered iron so I can remove it with a gold old backwash. It's the top-off I'd like to take care of. I've read the reviews on the Metal Trap and I believe that it will help reduce, but not eliminate, the soluble iron coming in. I've also read a few posts on people using small (RV sized) water softeners on their top-off lines. My question is, which will do the best job at removing soluble iron? It seems I can get a 16k grain water softener cheaper than the smallest Metal Trap, so... is that the way to go? It seems like it, but I'm concerned I'm missing something that would change the equation.

 

[Rancho Cost-a-Lotta]

I think @JoyfulNoise may be able to help out.

 

[JoyfulNoise]

It seems I can get a 16k grain water softener cheaper than the smallest Metal Trap, so... is that the way to go? It seems like it, but I'm concerned I'm missing something that would change the equation.

What you’re missing is the fact that the ion exchange resin used in water softeners becomes irreversibly loaded with iron and no longer will function after enough water has been treated. Ion exchange resins used for water softening (mineral ion removal) are designed to exchange sodium, calcium, and magnesium ions reversibly. Metal ions like iron, copper, manganese, etc, damage ion exchange resins. This is why iron removal filters (greensand) use a completely different chemical process for treating water with high levels of dissolved iron.

The metal trap filters will probably do what you need but they are consumable filters so you’ll be paying the expense of replacing them periodically. You should probably consider adding on a water flow meter/totalizer so that you can track how much additional water you are adding and know more accurately when it’s time to change the filters.

 

[ajw22]

DE filter will not filter out iron in the water.

Polyfill may filter some iton out.

Iron Fill Water Filter - Further Reading

www.troublefreepool.com

After an AA treatment the water should be drained or exchanged for iron free water.

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com

Draining - Further Reading

www.troublefreepool.com

 

[GaryParr]

What you’re missing is the fact that the ion exchange resin used in water softeners becomes irreversibly loaded with iron and no longer will function after enough water has been treated....

The metal trap filters will probably do what you need... You should probably consider adding on a water flow meter/totalizer...

OK, yup.... I was missing something. I've been reading non-stop about iron on this forum for a day or two and I guess it all got jumbled. Thanks for setting me straight. I'll go for the Metal Trap and a flow meter/totalizer.

DE filter will not filter out iron in the water.

Normally, no. But the "Sequestrant - Further Reading" page has this to say...

Can Sequestrant be Filtered?​

Jack's said that the combined HEDP-metal molecules will be filtered out of the water by filter media that removes particles 10 microns or smaller in size. This would include D.E. and Zeolite filter media. Coarser filter media, i.e. sand, requires the use of a filter aid like D.E. or fiber. Once the HEDP-metal molecules are trapped in the filter, the filter can be backflushed and the metals physically removed from the pool water.

.... so unless I'm totally misunderstanding (which is possible) then my sequestered iron will be banished from my pool after I backwash assuming I do that before raising the chlorine level back up.

 

[JoyfulNoise]

That article probably needs a lot more detail because it’s not quite right.

Long story short - if an iron ATOM is attached to an organic phosphate chelating MOLECULE, it CAN NOT be mechanically filtered as it still is a DISSOLVED solid compound. However, there are some very long chained organic compounds (poly acrylic acid based sequestrants) that can SOMETIMES form suspended solid aggregates that are capable of being filtered out. There is also the situation where some iron that is chelated by a chemical compound becomes oxidized and converted into a suspended solid (rust) that will tend to be filtered out by a small particle size filter. That situation is not common and it’s slow, so it doesn’t remove much iron at all.

 

[JoyfulNoise]

If you do an AA treatment you will be lifting the iron stains and converting solid iron (Fe3+ ion) back into its more soluble form of dissolved iron (Fe2+). A sequestering agent like HEDP will simply hold most of that iron in solution as a dissolved metal-chelate complex protecting it from oxidation for a period of time. The iron will stay in the water. There is no chemical way of getting it out of the water. So you have to drain the iron-laden pool water and refill with fresh water that has no metals in it.

 

[GaryParr]

That article probably needs a lot more detail because it’s not quite right.

The iron will stay in the water. There is no chemical way of getting it out of the water. So you have to drain the iron-laden pool water and refill with fresh water that has no metals in it.

Yeah, this is pretty much the opposite of what the article implies. I'm guessing that, in layman's terms, there is a chance that some of the sequestered iron can get caught up in the DE filter but not enough to really matter. Is that about right?

Question related to this. Will the Metal Trap remove sequestered iron? I'm considering using the submersible pump + Metal Trap method to reduce the iron content of the pool water. Not sure if I should do that before or after the AA treatment or if it even matters.

 

[JoyfulNoise]

Yeah, this is pretty much the opposite of what the article implies. I'm guessing that, in layman's terms, there is a chance that some of the sequestered iron can get caught up in the DE filter but not enough to really matter. Is that about right?

Question related to this. Will the Metal Trap remove sequestered iron? I'm considering using the submersible pump + Metal Trap method to reduce the iron content of the pool water. Not sure if I should do that before or after the AA treatment or if it even matters.

There really isn’t a lot of information on what the metal trap filter is composed of so there’s no way to know if it will remove chelated iron or not. I suspect it won’t as that’s not how iron filters work.

You’d be better off building one of those 5 gallon bucket filters loaded up with poly fill. If you can add a cal-hypo chlorine tablet to it, that would work great as the high pH and high FC inside the bucket along with the high surface area poly fill will cause the iron to precipitate and get removed. Poly fill alone works ok, but the chlorine tablet is what does the trick chemistry wise. It it has to be cal hypo NOT trichlor. Trichlor tabs are acidic and won’t cause the iron to precipitate.

 

[GaryParr]

I feel like you should run a class on this.

You’d be better off building one of those 5 gallon bucket filters loaded up with poly fill....

I considered the bucket before, but since most of my iron is in suspension, I overlooked it. Didn't think of adding a cal-hypo tab to force the precipitation. This is why they pay you the big bucks.

I wonder what the chlorination effect of this method typically is? Figure... 19k gallon saltwater, CYA around 75 and FC usually hovering between 4 and 5 ppm. So... shutoff the SWG and run through the bucket and the FC will start to jump, correct? Probably not bad and will just facilitate faster iron removal (and some staining I suppose).

OK, so that should go a long way towards lowering the iron content of my existing water.

Would the bucket+poly fill+cal-hypo method work as well or better (or worse) than the Metal Trap for topping-off?

Appreciate you letting me pick your brain!

 

[JoyfulNoise]

This is why they pay you the big bucks.

I demanded they triple my salary this pool season and they agreed to adding a few more zero’s to my pay ….

I wonder what the chlorination effect of this method typically is?

It’ll whatever the effect of adding chemicals on pool math says it will be. Since you’re in New England I imagine your water is already pretty low in CH. You may want to drop the pH and TA a bit to compensate for the higher pH from the cal-hypo. I’d leave the SWG running as the iron precipitation process really won’t impact it.

Would the bucket+poly fill+cal-hypo method work as well or better (or worse) than the Metal Trap for topping-off?

In my opinion, the metal trap scenario carries a pretty high upfront cost for an unknown result. The “bucket method” seems like a lower cost entry point which has a fair number of positive result associated with it. So Id likely opt for the lower cost/higher likelihood option.

Plus, no one has ever said. “Darn it! I have too many 5 gallon buckets …”

 

[GaryParr]

I demanded they triple my salary this pool season and they agreed to adding a few more zero’s to my pay ….

So very nice of them to meet your demands.

It’ll whatever the effect of adding chemicals on pool math says it will be. Since you’re in New England I imagine your water is already pretty low in CH.

Yup, 75. It's like you know what you are talking about or something. Ask for another zero.

You may want to drop the pH and TA a bit to compensate for the higher pH from the cal-hypo. I’d leave the SWG running as the iron precipitation process really won’t impact it.

In my opinion, the metal trap scenario carries a pretty high upfront cost for an unknown result. The “bucket method” seems like a lower cost entry point which has a fair number of positive result associated with it. So Id likely opt for the lower cost/higher likelihood option.

Plus, no one has ever said. “Darn it! I have too many 5 gallon buckets …”

Can I get an Amen!

Thanks again for taking the time. Hope you have a great day!