It's not that you can't QT a Rainford Goby, it's their diet that makes it difficult. They like to graze by sifting the sand and eating hair algaes, etc. In a spartan bare bottom QT they can literally starve to death.
But you can use sand in a QT. Humblefish posted on this. I'll give you the link below. So do you have sand that is "dirty" enough with material for your fish to eat from an established tank?
So the big question is what does yours eat? Some have got theirs to eat Hikari's really small pellets, some feed Formula 2 which is a frozen cube for vegetarian type fish.
I've never liked the bare bottom QT look, and have noticed how some fish seem uncomfortable in that environment. Especially sand burrowing wrasses, gobies and other fish who utilize sand as part of their daily routine. I've also seen tangs, angels, etc. fight their reflection on the bottom...
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