1 cube vs 2 half cubes?

I would err on the side of ‘NO’ rather than ‘YES’

Running the 2 tanks in series will mean the first tank will expire and the 2nd tank will be doing all the cleaning …

As we understand, DI RESIN is not like a material filter and simply ‘fill up and hold’ - it actually has a point where it starts releasing TDS to the water - and all that will be caught by the 2nd DI Tank - it is much the same result, however,

To make the system simple, and work the ‘Law of Averages’, I would recommend that you connect them in parallel … the tubing will require a couple of 'Y fittings …

In fact, we might just do this with the kits … at present we have the 2 x DI TANKS in parallel !

Did you know that you can get a 3 storey kit and a DI TANK, 2 cubes of Resin for under $1 a day ?

Is there any difference in doing two 1/2 cf tanks in parallel vs doing one full cf tank? Maybe if you need more flow, doing two 1/2 cf in parallel can give you more flow. But it won’t make the resin last longer or anything like that, right?

30 bucks a month? I’m listening…

Good post . I guess what I will do with my two tank set up is just keep an eye on that first tank, an once that tank gets to a certain tds change resin, an switch positions. My question is what tds should I look for in that first tank?

Perry Tait
So if I disassemble my two filter cart and roll with one filter like you sell, 1/4 cube, I should get about half as much water out of it? I think it will be easier to manage because it will be smaller and lighter.

Are you guys seriously still using single tanks??

A dual tank system will save you around 30% on resin costs - tried & tested, from personal experience.

It works like this:

2 tanks, one after the other. The first tank takes a big hit & the 2nd tank just polishes it off. Normally when your TDS starts to rise you’d throw out all your resin right? With 2 tanks you just throw out half, then you switch the 2nd tank round to first position. Its not giving you a zero reading any more, but it is taking the tds down below 10, so you keep using it untill its completely dead with the freshly refilled tank now in the 2nd position polishing the water down to zero.

The difference is that you keep using the resin until its completely dead - in a one tank setup you dispose of the resin when its still improving TDS - its just not improving it enough!

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So you have experienced a 30% savings and it’s not a theory? What is your average TDS? Do you run small or large tanks?

This explanation may hold true if your water sources varies a lot where one source may have more positive charged ions but then another source may have more negative charged ions. But it would not hold true if you use the same consistent water source.

For example, let’s say if you have a 50+/50- resin mix, but your water source is 70-/30+. In this case, the + resins will be spent up sooner but the - resins are still not spent and would get wasted if you decide to dump it all. But in the 2 tank scenario, you only dump half of the unspent - resins from the first tank, and you keep the other half unspent - resins in the first tank around, and rotate this first tank to become the second tank. So if you changed to a different water source next time that has more + ions, this unspent - resins in the first tank gets to be used up.

So yes, from this perspective, there may be an advantage to a 2 tank approach, but it may not be a consistent advantage if your water source is not varied like explained in the example above.

But there is also a disadvantage to this approach. Like Perry said, if the + resins are all spent up already in the example above and you rotate the first tank to become the second tank, this first tank will leach back out the impurities into your (new) first tank because its + resins are saturated already. So now your (new) first tank will not last as long as it should because this leaching of impurities will make it work harder to remove everything.

So this disadvantage may wipe out any savings you may have with the 2 tank approach.

So I think it’s best to not over analyze things and just keep it simple instead of trying to save a few bucks on resin with a 2 tank approach. I think that was Perry’s final conclusion.

Definitely not a theory - I used 19 litre tanks (Not sure what the cube equivalent is) after an RO with a TDS output of 017, so I was changing resin in one tank approx every 6 months.

Nope - the savings are not at all dependent on water type or quality - its simply that on a one tank setup you dispose of the resin before its completely spent. Your input TDS might be 200, but you’ll dump the resin when the output rises to 010,… the resin is still removing 190 TDS.

With a twin tank setup you only dump the resin when its COMPLETELY spent - and thats where you make the savings.

I heard that once the TDS hits 10 it goes up really fast. I was told to just replace all the resin in both filters on my cart because the savings wasn’t worth it.

The real question is how quickly the output will go from 0 TDS to 200 TDS. If it goes from 0 to 200 very quickly, then the advantage of a 2 tank set up is minimal. If it goes from 0 to 200 slowly, then the advantage is real. So the question is how fast it goes from 0 to 200?

Let’s assume that the water has only positive charged ions (for simplicity’s sake), and the resin has negatively charged beads to filter out these ions. Then once the negatively charged resin beads are exhausted, the TDS reading would jump up very quickly. You wouldn’t think the TDS reading would go up slowly if the resin is all spent. The reverse would be true if the water has negatively charged ions only and the resin beads are positively charged

But if the water has a mix of negative and positive ions, which is more realistic in real life, then one type of resin bead is spent but the other type may not be spent. So if you take a simplistic view that the first tank is still serviceable over all for a while longer, but that’s only true that it’s still serviceable for one type of charged ions in the water, but it’s really no longer serviceable for the other type of charged ions in the water.

That’s why the type of water matters. That’s why Perry doesn’t address whether a 2 tank set up last longer or not, because it depends. On the type of water. And that’s why the focus on his answer is about the type of water and the mix in the resin beads.

It looks like the new unger lite hydro power stage one would accomplish the same results as hooking up two 1/2 cubic ft tanks. I’ve been running two full cubic foot tanks and I think I’m going to switch to this when it’s in stock. Any idea on what the resin bags cost I couldn’t find replacements on the website

I use a mixed bed resin in both tanks and have used the setup on multiple water sources - I found a 25 - 30% reduction in resin usage wherever I was living.

That’s pretty impressive and I don’t doubt you. I was just trying to deduce how this saving can happen and I can see that happening on multiple water source with different ionic mixes. So your confirmation that you’ve used the setup on multiple water sources kinda confirms this.

Njones Nate when do you change your resin in your inlet tank .


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I assume you mean stacking up 2 HydroPower units so that you can quickly dump the bottom bag and move the top bag to become the bottom bag and put a brand new bag on top?

That’s a pretty clever idea, but I think the 2 tank setup here requires an inline TDS after the first tank so you’d know when to change it out and rotate the tanks. With the HydroPower, you don’t have the ability to measure the TDS reading between the 2 bags, so you don’t know when you can rotate the bags.

When the TDS output of the 2nd tank rises above zero i’d change the resin in the first tank & swap it to 2nd position - with a static production system in my garage and a big tank in the van I checked TDS every single fill, so usually caught it at 001 or 002.

I found best results with top quality virgin resin - I tried different brands & found Tulsion mb115 worked best for me - surprisingly Unger resin performs worst in my area!

Yeah, I think it depends on whether the mix of the resin is a good match with the ionic mix of the water in your area or not. If the mix is not a good match, even a high quality brand name may not necessarily perform better.