Why is My RO Water Green?

[DISCUS STU]

I have a Coralife 3-Stage 50 gpd system that I've been using for years.

When replacing the old membrane, the new membrane puts out greenish-yellow water for about the first 15-20 gals. that doesn't exactly look like something I'd like my fish to swim around in.

The RO membrane is a standard GE TFM-50 Reverse Osmosis Membrane. I also replace the carbon prefilter.

While this eventually clears up, can anyone give me a heads up on what this might be? Until now I've just thrown away this water.

Regards - Stu

[DJW]

I flush a good 20 gallons through a new membrane. They put a preservative on new membranes called Sodium Metabisulfite, which is supposed to be yellow, but who knows if that's what you are seeing. What you might do is check the TDS to see if its decreasing... once the TDS is steady the stuff should be gone.

[DISCUS STU]

Thanks Dan, sounds about right.

[Willie]

I'm not familiar with this system, but I have a Merlin R/O System that uses dual membranes. The membranes are packed in a sodium azide solution to prevent microbial contamination. Sodium azide is a poison at high dosages, so the instructions are clear to run the filter for 24 hours and discard all the water. I think you took the most prudent approach.

[DJW]

I use the Stealth RO200 and thought I had better check the instructions again. It says, "Flush the system for 30-45 minutes when the system is new and/or when you replace your membranes. This will flush out the food grade preservative in the membranes."

I flush it much longer than that, just to be on the safe side.

[Neptune]

yes, you always have to flush a new membrane in any RO system.