DI Resin

[Stu]

I recently purchased some color-changing DI resin from Bulk Reef Supply. The color (and I would guess effective "lifetime") of this stuff seems to be changing very quickly. My RO unit is not plumbed into my water line. Due to lack of storage space, I run it with a faucet/spigot adapter and fill up 5 gal. jugs. The previous color changing resin I had changed color slowly, and it lasted for a number of months. So far, I have made about 50 gallons or less with this stuff, and the color-changing line is already about 1/3 of the way up the cartridge. Is this normal? I just replaced the prefilter and carbon filter in the first 2 stages, and the membrane is only about 6 months old with relatively light use.

[DaveS]

mine changed really fast too, after about 150 gallons of 2-3 TDS water. But in looking at the TDS in/out, it is still decreasing which means the DI is still working. I've decided to ignore the color changing stuff and just rely on TDS readings to determine when to replace the resin.

[Origami]

Mine seems to be going through two color changes. The darker beads faded rather quickly, and now it's got a (layered) two-toned amber sort of look. And, I've noticed that one of the two tones is becoming more prevalent as time goes on. Since my output TDS continues to be zero, I've decided that this two-toned look is normal and that as the change to the banding continues, that this is likely the indicator of resin exhaustion with time. Monitoring your output TDS is best way to determine resin exhaustion.

[bbyatv]

I have gone through two 5 gallon bags of the same stuff at this point. I have found that the mew DI media splits in to two colors, tan up top and purple on the bottom. This does not mean that the media is spent. It just means that the color change is not longer reliable. I bought an in line TDS meter to solve the problem of knowing when my media was spent.

 

Here is a link to one at one of the WAMAS sponsor sites.

 

http://www.airwaterice.com/product/DM-2/DM-2-INDUSTRIAL-DUAL-TDS-MONITOR.html

 

This solved my DI media problem.

 

Bruce

 

 

I recently purchased some color-changing DI resin from Bulk Reef Supply. The color (and I would guess effective "lifetime") of this stuff seems to be changing very quickly. My RO unit is not plumbed into my water line. Due to lack of storage space, I run it with a faucet/spigot adapter and fill up 5 gal. jugs. The previous color changing resin I had changed color slowly, and it lasted for a number of months. So far, I have made about 50 gallons or less with this stuff, and the color-changing line is already about 1/3 of the way up the cartridge. Is this normal? I just replaced the prefilter and carbon filter in the first 2 stages, and the membrane is only about 6 months old with relatively light use.

[Brian Ward]

I, too, rely on an inline TDS meter and not on the color change. It's much more accurate.

[Stu]

I have an inline TDS meter and go by that reading, but I was just curious about the rapid color change compared with the last one I used. I was a little worried that the membrane wasn't operating optimally and the DI resin was working overtime to make up for it (hence the quicker color change).

[Brian Ward]

I have an inline TDS meter and go by that reading, but I was just curious about the rapid color change compared with the last one I used. I was a little worried that the membrane wasn't operating optimally and the DI resin was working overtime to make up for it (hence the quicker color change).

 

If you have the dual inline TDS meter (which is what I use) position 1 of them after the RO and 1 after the DI - that way you can see the effectiveness of both the RO membrane as well as the DI resin.

[Stu]

That's a great idea. Mine is a dual meter. I never really saw the use of the first reading (other than to inform me of the fact that my tap water has a lot of TDS). It's still going to be filtered out, just a matter of how often the media/filters are used up. Any idea what a reasonable TDS level is post-membrane, but pre-DI?

[Origami]

If you have the dual inline TDS meter (which is what I use) position 1 of them after the RO and 1 after the DI - that way you can see the effectiveness of both the RO membrane as well as the DI resin.

This is what I do, too. It'll give you an indication of when your RO membrane begins degrading, too. The lower the TDS is coming out of the membrane, the longer your DI resin will last.

 

I modified my setup last summer to automatically refill my RO/DI reservoir only once every 2-3 days. I did this by adding a solenoid valve (purchased from autotopoff.com) inline between my RO/DI system and the float valve in the reservoir. I trigger the solenoid using a programmable electronic timer that keeps a 1-week program. The idea behind doing this was to produce water less often, but in greater quantities since the initial TDS coming out of RO membrane is typically much higher than it is after it's worked for a few minutes. The result of this change has been remarkable. Where I was changing out my DI resin every 2-3 months, this latest batch has been lasted 7 months and is still giving me 0 TDS out.

[Brian Ward]

That's a great idea. Mine is a dual meter. I never really saw the use of the first reading (other than to inform me of the fact that my tap water has a lot of TDS). It's still going to be filtered out, just a matter of how often the media/filters are used up. Any idea what a reasonable TDS level is post-membrane, but pre-DI?

 

It depends on exactly which membrane you have, input TDS, water temperature, and pressure. I have gotten anywhere from 12 - about 85 TDS on the output from the RO membrane. Usually around 15-25 when my booster pump is running - which puts the pressure reading around 60psi.

[bbyatv]

I have my meter set up this way as well. One after RO and one fter DI. What you may find is that if you have the output of your RO/DI unit connected to you auto top off system, the TDS coming out of your RO is high. This is because if the flow rate is very low through the unit, the water may slip past the seal on the membrane. In order for the seal to work well, you need good flow and pressure. For this reason, I have set up a system as described in the following post:

 

http://www.wamas.org/forums/topic/40550-rodi-enhancement/page__p__342817__hl__bbyatv__fromsearch__1entry342817

 

Bruce

 

This is what I do, too. It'll give you an indication of when your RO membrane begins degrading, too. The lower the TDS is coming out of the membrane, the longer your DI resin will last.

 

I modified my setup last summer to automatically refill my RO/DI reservoir only once every 2-3 days. I did this by adding a solenoid valve (purchased from autotopoff.com) inline between my RO/DI system and the float valve in the reservoir. I trigger the solenoid using a programmable electronic timer that keeps a 1-week program. The idea behind doing this was to produce water less often, but in greater quantities since the initial TDS coming out of RO membrane is typically much higher than it is after it's worked for a few minutes. The result of this change has been remarkable. Where I was changing out my DI resin every 2-3 months, this latest batch has been lasted 7 months and is still giving me 0 TDS out.

[DaveS]

Just to add a few tidbits of info from my experience. I use TWO dual inline TDS meters. The 1st meter, I measure TDS from water supply going into system and TDS of water after prefilter and carbon block (before going into RO membrane). The 2nd meter measures water out of the RO and water out of the DI.

 

The first sensor on the 1st meter doesn't do much for me. Like you said, it just tells me I have dirty water that's going to get filtered.

 

The second sensor on the 1st meter tells me what the TDS going into the RO membrane is. That, along with the first sensor on the 2nd meter tells me how much TDS my RO had rejected. Your membrane has specifications that should say things like 98% rejection rate. So if your TDS is 100 into the membrane and 3 coming out, you know your rejection rate is 97%. As Brian says, the actual rejection rate will vary from the spec based on water temp, pressure and other things but you should be close. If not, something is wrong (I had to install a booster pump cause my 150GPD membrane only had 80% rejection).

 

Between the first and second sensors on the 2nd meter, I can compare the TDS before/after my DI chamber. As we have discussed, if the number is less after the chamber, your DI is still working.

 

What some people don't do is monitor the membrane. They look at the output of the DI, see zero, and are happy with that. But the DI has a fixed number of dissolved solids it can take out before it is exhausted. Regardless of whether you put in 2 TDS water or 20 TDS, you'll pretty much still get zero TDS water out. BUT your DI resin will only last 1/10th the amount of water (time). Therefore it's important to make sure your RO membrane is functioning properly in order to prolong the usefulness of the DI resin.

 

As Tom mentioned, startup output for the RO is bad. Once it gets running the TDS out drops to steady state levels. That's why it's much better to have the RO/DI filter run for few long periods than more short periods. I have a low tech version of Tom's fill system. I have the standard float valve at the top of my top off chamber which stops the RO/DI when the tank is full. I just added a small ball valve from Home Depot to the water line input of the RO/DI. When the tank is full the water stops and when I notice that, I shut off the water supply. When the water in my top off gets low, I turn on the water supply letting it make 25 gallons at a time. Once it's full, I shut off the supply again. Basically it's a manual version of the solenoid. But since my evap is 1-2 gal/day and the 25 gallons lasts 1-2 weeks, I don't have to do it very often.