Hmm... this is going to be tricky.
I believe it's either a sleeper goby(subfamily Eleotrinae), possibly one of the Dormitator species. Thing is that gobies of that species spend more time swimming in open water than bottom dwelling... which appears to not apply to you.
Another suspicion is the genus Acentrogobius, check out Acentrogobius viridipunctatus. These gobies have emerald green dots on their flanks and I can't tell from the pics if yours has those but the body looks shape looks similar.
If it was any longer in I would almost start looking into it being one of the more primitive, fully aquatic species of mudskipper, but I highly doubt it. It's just that it's face shape and eye positioning is very mudskipperish. Then again, they're part of the goby family subfamily Oxudercinae.