If you look there on the left sided my tank that's Falkor my 13" violet Goby! He became more active when the last humpback goldfish died bc he was no longer getting picked on. If you have mid to high level dwelling fish in your tank,he might be getting bullied. Even by smaller fish. They're peaceful goober fish that are basically blind, nocturnal, and just wanna chill. Falkor is MOST active at night. He can sometimes get crazy with that tail. I've been splashed more than I like bc I'm sure you've noticed they like to swim backwards. I'd say to keep an eye on his tank mates and if he's not getting picked on or having to fight for his food then maybe you should try taking a look at your tank around 1am lol! (Just don't turn on any lights near the tank, they'll immediately drop to the bottom and "play dead")
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