well first i would try to get him another friend he might just need a few of his own species, and i might try live food instead, and you could go get some salt from your lfs (local fish store) and get some salt for sick fih it helps them get used to their new home and helps with any sicknesses the might have. also it is safe with all yor fish.

p.s. what size tank and fish do you have bsides the goby?

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tanks

55 gal.

1 gold ram
1 male krib
2 coolie loaches
6 serpae tetras

10 gal.

15 krib fry

10 gal.

1 gold and some tadpoles.