i was wondering because he seems to be mixing some brackish fish with freshwater ones. the bumblebee goby is definitely brackish...he wont do to well if your tankis completely freshwater and your other ones wont do to well if you make it brackish....hmmm.
I use completely freshwater R/O. I bought a bumblee goby more for a test. I've had him for 6 months now and he's stay colorful.