I'm sure more knowledgeable members will chime in but my question to you is... did you acclimate the pair and if so how? This means you knew the parameters of the tank they came from and drip acclimated them to you tank's parameters. Also, were you able to see them in their tank at the store to see if they looked healthy?
@xnaz I’m really sorry to hear and see this. The goby looks really thin — it could be the pictures. How was it doing at the LFS, and how were the rest of the fish?
I was at a LFS just recently, and in each tank there were healthy looking fish and also several dead fish. I’m really not exaggerating it was really sad and also made me angry. I turned around and walked right out. I figured if they couldn’t maintain their tanks enough to take out the dead fish then they really didn’t care about the fish that were living.