DKoKoMAN’s 305g Basement Reef

[Myka]

This is totally normal on start up. If you placed a TDS sensor between the RO and the DI you would notice that the first blast of water will typically be about the same TDS as plain tap water. The DI resin will not catch all of it so you'll see some in the product water. This is one of the reasons why it's so important to run the RODI for long periods rather than short periods and why your fish RODI should never be hooked up to a pressure tank.