RODI unit needs maintenance?

[CorvetteJoe]

I got my RO/DI unit a few months ago and everything was doing fine.

I bought it used and bought a new prefilter, charcoal filter and DI membrane. The RO membrane is original from who knows how much usage.

 

I also have one of those dual digital TDS meters.

 

I've only ran maybe 30ish gals through the thing in that time (filled a few 5gal jugs for fish water and some drinking water pitchers for the fridge).

 

The tap water is at a steady 140ppm.

The final DI output has been very steady at 0ppm.

 

Today though the final DI output sits at 20ppm.

 

I opened up the waste water flow valve to flush some water through it, and the final DI output drops to 5-7ppm.

 

I moved the 1st TDS sensor to the waste water hose and it also reads 140ppm when flowing (this would be after the RO membrane. When I close the waste water flow valve to build pressure, it jumps to 200ppm for the waste water and 20ppm for the final DI output.

 

Whats going on? Do I need to replace the RO membrane?

 

 

Sorry, this is kind of confusing. If anyone has any questions to better figure out the solution, please ask.

[dtfleming]

you need to replace the DI resin and prefilters. I would replace those first and then see what your tds comes out to before you replace the RO membrane.

[CorvetteJoe]

you need to replace the DI resin and prefilters. I would replace those first and then see what your tds comes out to before you replace the RO membrane.

 

I just replaced the DI resin and prefilters a couple months ago and have hardly used it... would they go bad that quickly? My tap water isn't that bad I don't think.

 

The RO Membrane has never been replaced as far as I know, and I don't know how much use it got from the previous owner.

 

I am guessing the waster water flow restrictor with valve is a flush valve, as it lets the water run through really fast. That said, It's always flushed before use to bring the PPM down before I start bottling the output water.

 

Hrmm... I guess I'll order another DI and prefilter kit

[dtfleming]

how long did the other owner have it. I replace my prefilters and di resin every 3 months. The RO membrane should last a year or more. If replacing them doesnt work then the membrane will need to be replaced.

[CorvetteJoe]

how long did the other owner have it. I replace my prefilters and di resin every 3 months. The RO membrane should last a year or more. If replacing them doesnt work then the membrane will need to be replaced.

 

Ahhh ok. I didn't think they would need to be replaced that quickly. Perhaps I've had them longer than that.

 

How many gallons do you run through yours every period?

[dtfleming]

Prob around 300 or so gals in 3-4 months

[CorvetteJoe]

I don't have anywhere near that amount.

 

I wonder if it sitting for periods of time (I think the sun even hits it for part of the day, it sits outside) has any effect on it since the water just sits in it.

[hcsceo]

r u saying that your water after the RO but before the DI is reading 140? If that is the case I'm sure it is your RO membrane. You need to test the water before the RO, after the RO but before the DI, and after the DI to get a good feel for what the problem is. Testing water before the RO and after it goes through RO will give you a percentage of membrane effectiveness. You should be 96% or better at all times. For instance my water tests at 480 at the tap, 16 after the RO (giving me 97% effectiveness), and 0 after DI. Your DI cartridge should last 400 gallons without issue. It'll take 10 gallons just to get it broke in so I can't imagine that is the problem. I suspect you have a bad RO membrane but only testing water right before it enters the RO unit and after the RO before the DI will tell you that. Testing the waste water going to the drain from the RO tells you nothing. Hope this helps.

 

Steve

[hcsceo]

One more thing. My membrane is 3 years old and still kicking. I think it really depends on how many gallons go through it, whether you flush it, what the water quality is before going into the unit and whether you are keeping up with carbon changes. Remember that clorine will kill a membrane as soon as it hits it so make sure you carbon cartridge or cartridges are replaced regularly. My system has a sediment cartridge, two carbon cartridges, then the membrane then the DI. I like to use Extruded Carbon as it is supposed to be better.

[r20crazy]

buy a new RO membrane. also make sure water isn't chaneling through your DI resin. you may need to 'stir and/or repack' it to prevent this. I'd replace the membrane since you have already replaced the other filters, this way you KNOW it is good for a year or more with no worries

[disaster999]

i think hes taking about 140ppm for the waste water when hes flushing it and 200ppm when it closed the valve to flush the RO membrane.

[CorvetteJoe]

Thanks for all the advice guys.

 

I read in another topic about anything under 20ppm is acceptable for the water, so I am going to continue messing with it. I just made another 2 batches (2 x 5gal containers) of water, one around 7-10ppm, the other around 10-15ppm. I guess that will buy me a little time to test the water out at different places before purchasing anything.

 

I am most likely going to go with the RO membrane since I don't know the history of it being a used RODI unit and all.

 

One note on r20crazy's comment about the DI resin channeling water... I have a sealed throw-away DI tube that is somewhat translucent. I can see the inputside is darker than the output side and there is some air in there. I can shake it up and watch the bubbles move around. I set it upright (exit towards top) and noticed the bubbles channeling through only certain little paths in the resin before making it's way to the top. Being that I can't open the tube up, I guess I can try shaking it a lot to stir it up the best I can? I am thinking its compacted on one side and not so much on the other.

[r20crazy]

if its sealed (DI canister), shake as you stated, thats about all you can do. having the di vertical instead of horizontal helps to avoid the chaneling (sp?).