I think you should be fine adding one. I have a much larger tank but I have 2 gobies in mine, a pink spotted watchman and a brown barred goby. I also have a lawnmower blenny in there and they all live together fine.
As long as there is enough rock spots for them to hide and/or burrow you should be good.
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.