Sorry,a qrc(quick release connector) is the hoselock type connector that pushes on to the end of the ionics di canister so the water can pass through it.
To test if your ro is okay take a tds reading after the water has been through the ro. To do this just disconnect the di canister and take a tds reading with a handheld tds meter. If your tds reading is low then its okay. If it is high then eit the ro needs flushing, if that doesn't work then there could be a problem with the ro membrane.
But the first step is to check the tds level after ro.
Art