RO/DI Conundrum


Reefer Always Learning
Manhattan Reefs
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Have a 4 stage RODI unit. Changed the filters and membrane about 2 weeks ago. Tossed the first 5 gallons. Next few batches TDS meter rang out 0. Beauty.

However, recently my TDS has been reading 20 for the pure, 80s for the waste line and my tap reads at 56!

What could be the issue? How could my tap have less TDS than the RODI waste? And after changing filters so recently, how is my "pure" water so high?

Just recently tested a new batch of RODI salt water and the nitrates and phosphates were almost non-existent.

I only ask because my nitrates have been stubbornly high in my tank (between 50 and 80mg/L) so I was searching for reasons. Stumbled across this.

Bad TDS meter? Faulty RODI unit? Faulty filter replacement?

I'm at a los

greg 45

Active member
Manhattan Reefs
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bayonne / nj
If you have no nitrates or phosphates coming out of your ro/di you have a issue in your tank. Google high nitrated and see where they are coming from in the tank.


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Freehold NJ
You might try re-seating your membrane and make sure it went in all the way. Thats the most common issue after a change. I ise a pair of needle nose pliers and twist it as it goes in. Good Luck