It is the removal of mineral ions by using the ion exchange process. Using a mixed bed of anion and cation resins; ions, salts and minerals can be entirely removed from water.

The RO membrane has a direct impact on the life-span of the DI. The RO membrane can remove about 95-99% of TDS (minerals) in your water. When a DI is used after the RO membrane, you can expect almost 100% removal of the TDS.

First of all, there are two kinds of DI filter cartridges; vertical and in-line. Both can filter out the TDS down to zero (or very close to it), but they have different filtering capacities.
To figure how long they'll last is simple math. Take the capacity of the DI filter and divide it by the TDS of the water feeding it. The lower the TDS feeding it, the longer the DI will last. This is why it's good to have a RO membrane to remove most of the TDS before using a DI.

For Example:
The vertical DI has a capacity of 6,800 ppm. The in-line DI has about half that capacity, so around 3,400. Let's say that the RO is reducing the TDS down to 20. This is what the equation will look like for each DI:

Vertical DI:
6,800 (ppm) divided by 20 (ppm) = 340 (gallons of pure [-0- TDS] water)

In-line DI:
3,400 (ppm) divided by 20 (ppm) = 170 (gallons of pure [-0- TDS] water)

There are some exceptions to this equation. Higher than usual levels of some TDS can cause the DI to exhaust faster. It's also important to know when to flush the membrane before starting to make RODI water.

Some examples of elements that, if in high levels, can cause the DI to exhaust faster are: phosphates, nitrates, silicates, salt, calcium, etc. The RO membrane can remove most of it, but the DI would have to work harder than usual to remove it all from the water.

If the unit has sat inactive for more than one day and you do not flush off the membrane before making RODI water, it can cause the DI to exhaust faster as well. Make sure to flush off the membrane for one minute per day of inactivity. This doesn't really apply to those who use their unit every other day or every day. However, if you use it that much, you should still flush the membrane off once a month for about 30 minutes or so.

Instructions on how to flush are in the Fittings FAQ.

No, it's nothing to worry about. As long as there's water flowing through the DI, it doesn't really matter. It's air trapped inside of the housing. If you don't like how it looks, you can unscrew the housing a little to release the air. When the water fills the housing/chamber tighten it down quickly to avoid a small blast of water everywhere.

What happens if it fills back up with air after I do this?

Just repeat the process. It will eventually stop filling with air and leave the chamber full of water most of the time. If not, then it's still okay.

Yes, a DI cartridge can be used as a stand-alone filter. However, the lifespan will be reduced greatly (unless your water is very low on TDS to begin with). Just refer back to the DI life section of this FAQ.

Normally, a stand-alone DI is used in either lab or car washing applications. Though you can use our DI filters for these applications, we do not normally recommend it. We might refer you to a different company for DI filter units that were made specifically for these applications if we do not think that ours will last long enough for your use.

Typically, you will want the mixed bed resin. However, you can use separate beds (anion and cation) as well.

This is a simple process. Simply remove the DI cartridge from the housing. On the bottom of the cartridge is a screw-on cap. Unscrew it and remove the foam piece. Dump out the old resin into a garbage can/trash bag. Fill up the cartridge with the new resin and put the foam piece back in place. Screw the cap back on and you're done!

CAUTION!! - Resin is a very round material. Be careful not to get it into your eye. If you do, flush out your eye for about 15-20 minutes. Also, if it gets on a hard floor, be careful not to step on it because it can cause you to slip.

A water softener is needed if your water is hard. Hardness is able to get through the pre-filters and clog the RO membrane over time. Hard water starts at 4 GPG (grains per gallon) or roughly 68 ppm (hardness).

If you don't know if your water is hard, you can request a water quality report from your city/county. You can also have it tested by someone else. We offer a free testing of your water for TDS, hardness, iron and PH.

You can use a softening pre-filter (cartridge) if your hardness is less than 10 GPG. We offer them both in vertical and in-line cartridges. If you have more than 10 GPG, you will need a whole house softener. We do not deal with whole house softeners anymore. We will be able to let you know where to get one, but cannot recommend one over the other.