There’s a great thread at REEF2REEF. We’ll call it The Mystery of the Non-cycling Tank. For weeks, the tank owner had been trying to get his tank to cycle but to no avail — which is super weird. I mean, cycling is the one thing we can’t screw up right? Biology and chemistry are going to do their thing.
User “Brew12” works with him for weeks to try to figure it out, and they eventually start narrowing it down to the RODI water he’s using. He mentions that it “smells like chlorine,” but they don’t think anything about it. He’s using an RODI filter designed to filter out not only chlorine but also chloramines (which more and more water systems are using), and the TDS reading is 0. The water wouldn’t seem to be an issue.