View Full Version : Tunze Osmolator Eating Up My DI Resin?

10/07/2016, 04:57 PM
Pretty close to finishing my build, with just a couple of problems to iron out before we throw in some live rock and sand.

One big issue is that my DI resin is getting torn to shreds. I am literally going through a canister of that stuff every two or three days.

When things were first set up, and we were mixing saltwater to fill the tank, I was pumping 50 gallons of RO/DI water at a time into a mixing reservoir. As expected, only a small amount of resin was used up. I monitored the TDS levels throughout this, and the PPM levels stayed fairly stable at ~300 tap water, ~5 post RO, and 0 post DI.

Once the tank was filled up, we fired up the Tunze Osmolator, which is running off of a solenoid tapped into the DI output. A few days later, I noticed that the first DI chamber was exhausted, and the second was showing some wear.

During this time, the only thing that was coming out of my RO/DI was top-off water.

I started monitoring the TDS levels a few times a day, and here is what I noticed... if the unit was in "passive" mode, IE, nothing was going through it, the post RO levels went up to ~100! When the Osmolator kicked in, it eventually went back to the normal level of ~5, but it took close to a minute.

My guess is that it is the high TDS level for that first minute or so (times however many cycles the Osmolator goes through per day) is what it exhausting the resin.

Has anyone had something similar happen, and if so, how did you deal with it? My thinking is that I have to minimize the number of cycles the RO/DI (not necessary the Osmolator) gets hit with per day. I think there are a couple of solutions:

1. Put the Osmolator on a timer, so that it only fires up every six hours or so. The DI resin will still take a hit from that initial high TDS RO water, but it will be much less frequent, so the resin should last longer, although how much longer I am not sure.

2. Get a reservoir for the DI water, and feed the Osmolator directly from it. This way, it would only fire up the RO/DI when the reservoir needs filled. My main problem with this is that it doesn't seem friendly to my goal of automation, because if I'm using just a single float switch, it seems like the exact same thing would happen, where the reservoir is tapping the RO/DI unit multiple times per day as the Osmolator uses the water up.

I do have an Apex, which I know I can use for solution 1.

If there is a way to set up a DI reservoir with an Apex in which the reservoir would only fill when it is, say, 25% full, as opposed to keeping it 100% full all the time, that would seem to be ideal... maybe use two float switches, but that is learning curve central, as I'm still an Apex newbie. Otherwise, the second solution would probably have to be manual... I turn a valve when the DI reservoir is close to empty.

Thanks, all!

10/07/2016, 05:08 PM
If you want to automate it then another float switch is a good option..
As stated set it to trigger when the reservoir gets really low so its making enough water to keep the RO from cycling so quickly..

Not sure how much water you replace daily but I simply fill up the reservoir manually on my tank.. Its a once a week thing I just do on the weekend when I do my water changes..

gone fishin
10/07/2016, 05:17 PM
Rapid cycling will deplete resin fairly quick along with shorten a RO membranes life.

I had an old JBJ ato laying around that I put in a 10g brute for topoff water and the osmolator pump in the brute. This extended my DI resin life quite a bit. Good luck just my 2 cents.

10/07/2016, 07:21 PM
You basically have 2 choices.

Make RO/DI in batches and use a pump on the Tunze instead of a solenoid.
Add a timer that toggles a relay after 60 seconds or so. The relay would be a double throw where the NC is hooked to a solenoid on a T that goes to the drain. The NO would go to a solenoid after the T and leads to your tank. So you would have a total of 3 solenoids, 1 on each leg of a T. This would flush the high TDS water and prevent your DI resin from getting used up.

If you are doing any solenoid based version (even what you are using now), be sure to add a backup float switch in case the Tunze fails open crashes your tank and floods your house.


10/07/2016, 09:17 PM
ditto to the above comments. If you need to see it for yourself, get a TDS meter and mount it between the RO output and the DI canister and then watch the TDS as you first start the system. It will be up at several hundred and then drop down to its final level over several minutes.

Even though the TDS drops fairly quickly, that first bit uses a disproportionate amount of the membrane. If your steady-state TDS is 10 and the TDS starts out at 300, that water is using the DI resin 30x faster. In other words even if only one cup of water goes through at 300, it depletes as much resin as 30 cups of water. Now repeat this every time you turn the system on and it's easy to see what's happening to the resin.

10/08/2016, 05:58 AM
Tds creep kills DI resin. I put a tee in before the di and a valve so i can bypass the di resin until my tds comes back down. Wont work as easily in your case if im reading tjis right.

Buckeye Hydro
10/12/2016, 05:02 AM
Yes - short cycling will cause a situation where a high percentage of the water reaching your DI resin is high TDS ("TDS Creep") water. Here's some data from test runs with a 75 gpd Filmtec membrane:

If you fill a reservoir periodically so that you can be physically there when the system kicks on, consider a DI bypass valve to send the TDS creep water to drain.


10/18/2016, 03:57 PM
I ended up having my Apex turn it on for 15 minutes every six hours. It's definitely making a difference... the water level stays put, and it's not tearing through the resin as much. I'm guessing it's still more than it would be with a reservoir, but for now I can live with it.