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I've run into a strange situation - trying to figure out what exactly this could mean. I am using a 75gpd BRS ro/di unit with built-in dual inline TDS meter. I am getting 8 TDS after the RO (for those familiar with the BRS units, the "in" position on the TDS meter). However, I am seeing 28 TDS after the DI (the "out" position").

How can the TDS possibly go up instead of being the same or lower after the DI cartridge? Possibly a contaminant that has entered the DI cartridge somehow? A DI cartridge that is so worn out that it's breaking down? I have no idea, just thinking out loud I guess...

I've already ordered a new sediment filter, carbon block and DI cartridge and should have everything by Tuesday. The unit is only about 7 months old though, so it's not like I abused it or anything. Have not made anywhere near the 6,000 gallons of water I'm supposed to be able to prior to changing cartridges, and water pressure is good and stable at around 60psi going into the unit.

Thanks,
Matt
 

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When DI resin becomes exhausted it starts releasing the contaminants it has captured so the treated water can actually be higher TDS than the tap water was to begin with.
Always monitor your TDS and replace the DI cartridge or resin as soon as you see any evidence of TDS in the finished water.

I would highly recommend getting an handheld TDS meter to test your water. They are much more accurate dur to being truly temperature compensated plus you need a minimum of three TDS readings to troubleshoot a RO/DI system, tap water TDS, RO only TDS and finished water TDS. It takes all three and the dual inline only has two probes. I have two dual inlines but never even turn them on, I always use my handheld for accuracy.

replace your sediment and carbon block every 6 months like clockwork and disinfect the system at that time to keep things sanitary. I would also recommend better filters than BRS uses, at least a 1.0 micron sediment filter and absolute rated is much better than nominal rated so it protects the billions of tiny microscopic pores in the carbon block. 5 microns is about as effective as a screen door when you consider you can see 40 microns with the unaided human eye.
 
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