RODI Water sitting at 6 TDS

[Areseebee]

I have a new RODI unit for my tank. It's a "Maxwater" 100 GPD unit 6 stage. It's this one:

My input water is 230ish TDS. I am getting 6-10 TDS coming out of the unit. At first I thought it was just been breaking in but at this point, it's probably made 50-100 gallons without changing. I'm attaching a little picture of the unit itself, one thing is that I'm kind of surprised just how clean the first three stage canisters look. I'm used to them getting brown pretty fast, I suspect maybe the water is skipping those chambers? Anyone have any ideas how to troubleshoot this?

 

[BaliReefBox]

wrong reply

 

[Gtinnel]

First off do you know what the tds is after the membrane but before the di, and then what it is after the di? Knowing the tds after the membrane can help determine if the issue is more related to the membrane not removing enough tds, or if it’s the di that isn’t removing the last small amount of tds.
Also, most of these cheaper Amazon systems will have a post di filter that I would personally remove. It is usually to make the water safe to drink, but generally wouldn’t be used for an aquarium. I am also not sure if it increases the tds of the water.

Having the di resin canister horizontal is not ideal. Its easy for the water to only flow through the bottom half of the resin and deplete it while the top half appears fine.

 

[Areseebee]

I will measure those tonight. Perhaps it is the last compartment. It says something about coconuts and adding ppm. It also says it goes away which I thought it would have by now. I'll just remove it and see what happens. If that doesn't fix it I'll try measuring a couple points in the process to see

 

[Areseebee]

Ok yeah dumped all my water, got rid of the last canister and now it's 0. Hurray

 

[Jedi1199]

Make sure that every time you test for TDS, you use an absolutely clean container and draw your sample directly from the output of your unit. It only takes a couple minutes to fill a clean, dust and lint free specimen cup a couple inches deep. Then test your water. Even a light film of dust will throw off your TDS tester. I use 4 oz specimen cups, freshly washed and dried with a clean lint free towel (paper towels leave lint) and then hold the output tube into the container till I get enough to test with.

 

[Areseebee]

Yeah I thought about that. I figured that I could wash a vessel with my "dirty" RO which read at 8 and just get enough water out that I was going to dilute 100 or 1000:1 then the non-zero contamination would be minimal.

I considered buying an inline meter too but ended up feeling like this was enough.