Fish in QT dying

[ALang]

I don't know...Gobies are pretty fragile little fish.
Were they sick to begin with? If not, I would have just QT them in your hospital tank for observations and NOT dose them with any drugs until they show signs of diseases.
Next time, I'd just QT for a couple of weeks (or 4, for all those purists out there), without any medications. Just keep your water parameters top notch. If they don't show any sighs of illness, and that they are eating, and getting fat, then they'll be ready for your display tank. Gobies may want a little sand too.