What TDS is ok?

[Urban_Squrill]

I just got a used seachem ro/di unit. The unit was not used for about 8 months. I figured that I would need new membranes and filters. I kicked it on today just to see if my TDS meter works. And my meter was reading 350 ro and between 3 and 4 at the out put. Is 3 or 4 ok? Should I even use these membranes?

 

[theop]

Was the 3-4 ppm a reading from the output of the RO or the DI? If from the RO then that is 98-99% rejection so I'd say the membrane is working fine.

If not, then you need to measure the TDS from the RO unit output.

After the DI unit your TDS should read zero. If not you should replace your DI resin.

 

[AZDesertRat]

You need 3 numbers to determine the condition of the unit. Tap water TDS, RO only TDS without DI and finally RO/DI TDS. You are looking for a 96 to 98% rejection rtae from the RO membrane so if the incoming is 350 you should be seeing no more than 7 to 14 from the RO only. The lower the better. After the DI you should be seeing 0 TDS. Generally I change DI cartridges or resin when I begin to consistently see a reading of 2 TDS. When DI hs reached its capacity it begins to release contaminants back into the treated water and its the most weakly ionized substances thet get rleased first. These include things like nitrates, phosphates and silicates none of which you want.

Odds are the DI resin is shot especially if it was allowed to dry out, even when stored correctly it only has a shelf life of about 6 months. The RO membrane may or may not be OK, if it sayed wet it may be all right. TDS numbers will tell the story.