[ichy]

I am totally new to RO/DI units. I just set mine up.

I have a fourth stage with a DI canister in it and the directions say it changes color as it expires. It is golden brown now. What color will it change to as it expires?

 

[DaveK]

Usually if you look at it new color changing media is sort of a blue / brown, going to all brown as you use it. You'll see a line of color as you use it.

But there is a better way to see if its working. Get a TDS meter. Water coming out of the RO unit should be under about 8 ppm, after that goes through the DI part it should be under 1 ppm.

Here is an example of an inline TDS meter. You can monitor the water at two points - HM Digital Dual Inline TDS Meter

Here is an example of a hand held TDS meter - HM Digital Pocket-Sized TDS Meter w/ Thermometer

I check the output from the DI unit. It's usually at 0. When I see it go above 1 I know it's time to change the media.

A few notes -
For FW you may not strictly need the DI unit. Some people use valves and a T so they can bypass the DI part when getting water for use in FW systems.
You can get a refillable cartridge and bulk DI media from places like Bulk Reef Supply. It's a lot less expensive that way.

 

[ichy]

Thanks for that info! Its all brown, the unit is new/used but has been sitting in the box a long time. I think its bad.
I looked at those meters, I'll add one and a flush valve at some point.

Yep, saw the bulk stuff. BRS is right down the road from me so I will pick some up tomorrow. At about $19 for a refill and refillable canister, I'll just replace the one and not deal with it.

Bump: Another question.
BRS has a two and three probe TDS meter. What would the third before?

I get two, one on the in, one on the out. Does the third go between the 3 and 4th stage?

I just bought an online meter
off evilbay, the seller was eseasongear

They had it for 29.99 with free shipping or make an offer. I offered $25 and he accepted so $25 for the meter TYD was a pretty good deal and worth it, I thought,

 

[DaveK]

Just a note, not all DI media changes color with use. The material that doesn't change color is less expensive. So if you have a TDS meter, you can use the non color changing media.