What size tank do you have and how long has it been up?, always the first questions. lol
What do you have as far as a cover, an actual plastic cover or netting? I've been having an awful time this month as far as jumping fish. I will be going down to 1/4 inch netting and hopefully that can help with jumpers.
Is it possible the sixline is chasing the goby? I know my sixline is a tad aggressive so maybe yours is as well. I also have a flame hawk but all he chases are the hermit grabs. lol