A goby's aggression is basically it opening it's mouth in a manacing way and thats it. lol I plan on adding a yellow clown goby to my 20g that already has a green goby.
I also had a diamond back goby and a pinkspotted watchman in my 25g together for a few days and they had no issues at all.
Just keep the shapes and colors different and I think you'll be fine.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.