R/O unit and TDS

[randythereefer]

So I have an RO DI unit. I change all 4 cartidges about every 3 or 4 months. My question is this. I have a TDS meter and my water before all 4 stages is about 300 PPM after the DI its about 2 ppm which is great. But my DI cartridge didn't last very long this time. I went from a 50 gpd to a 75 gpd DI cartridge. My TDS before changing to the 75 was about 56 ppm from the RO unit after upgrading it was about 70 PPM. Is this okay? I mean how long does a RO normally last? Shouldn't my RO membranes takes the TDS down to about 10? I was confused by reefcentrals article on RO/DI units. Some suggestions are greatly appreciated.

Thanks in advance!!

 

[Scooterman]

I try and keep my TDS down to 0 at most 2, the RO should last a real long time, guessing a few years according to the instructions I've read. How much are you making & how many gph is your system rated for? if you replaced all of the cartridges it will take a while before the membrane is at saturation, then it will start producing more water. I don't know why your getting such high TDS's where are you getting the replacement cartridges? What micron size are they rated for? I use .5 micron carbon block & pre filters, makes a big difference, I would go at least a 1 micron or better.

 

[wrightme43]

This may sound strange, a friend had a water line burst downstream of his house. It filled the lines with clay and silt. It ruined his ro membrane, after it clogged the heck out of the prefilters too. Sometimes if the prefilters are not changed often enough, it will damage the membrane. Also I have noticed if I change my prefilters and my di resin at the same time, it uses up lots of the di resin, if I run the new prefilters with the old di for a while, then change the di it lasts longer. I dont know why, I have some guesses but who really knows. Steve

 

[NaH2O]

How old is the RO membrane?

 

[mlheppl]

If you grab a sample after the pre filters, after the RO and after the DI cartridge and check the TDS after each stage, it will help you to pinpoint where your problem is. If you changed your RO membrane when you changed the filters, you may want to make sure that you plugged the inlet hose to the inlet of the RO membrane and not the outlet of the RO membrane.

 

[randythereefer]

The RO membrane is about 3 months old but it read the same when new as it does now. I always replace all filters at the same time. I just seems that my RO water always reads kinda high. I'm just not sure when I should replace them since they always read about 50 ppm any RO filter. When I buy RO water from culligan it only reads like 5 so I can't seem to understand what the heck is wrong with mine. My water before any filter is abotu 300 ppm tds. I hope this helps.

thanks,

Randy

 

[dwall174]

I went from a 50 gpd to a 75 gpd DI cartridge.

Did you mean a 50 gpd to a 75 gpd RO membrane?

My TDS before changing to the 75 was about 56 ppm from the RO unit after upgrading it was about 70 PPM. Is this okay?

No it should be around 6~8 TDS after the membrane!

When you first set it up did you check to see if you were getting a 4 to 1 waste ratio? It sounds to me like your flow restrictor was not set right! Also when you got the new membrane you should have also replaced the flow restrictor with one that matches the gpd. of the new membrane.

 

[dwall174]

If you grab a sample after the pre filters, after the RO and after the DI cartridge and check the TDS after each stage, it will help you to pinpoint where your problem is.

A TDS meter won't help you figure out when to change the pre filters or carbon filters!

A TDS meter actually reads the electrical resistivity (conductivity) of the water. Hard water which usually has a lot of minerals in it is normally higher in TDS because of these minerals. A TDS meter will tell you that there are impurities in your water & if your RO membrane is working ok! And it will also help you tell when it’s time to replace your DI cartridge, But to know what’s in the water like Phosphate, Nitrate, & Silicate, you will still have to run individual tests. There are several forms of ionic phosphates & colloidal silica that are non-reactive & thus don’t show up on a TDS meter! Of course these are also the hardest to get rid of! Here’s a article on How A TDS Meter Works Which helped me understand it better.

 

[MikeS]

A good tip to increase the life of RO membranes and DI cartridges...install a water softener before the RO/DI unit (or install the RO/DI unit to take in softened water if you already have a softener)...the softening process helps remove a lot of stuff thats hard on the membrane, like calcium, ect.

Mike

 

[randythereefer]

I've come to the conclusion that:

1) My plastic housing is cracked somewhere letting bad water get in with the good.
2) Or I put the RO membrane in wrong somehow?? (I'm not sure how I could have done that).

I think I'll check the membrane tonight. I wonder how I could have put it in wrong? Maybe I didn't push it enough? I can't imagine getting it backwards but who knows. Any other suggestions are appreciated.

 

[Scooterman]

I'd go through it again and check the restrictor also, you never know.