I got my first GBR in my 30g for about a month now and he's one of my favorites! I'm wanting to get a Kribensis also but worried there's not enough space in a 30g? It's heavily planted and there's several hides to choose from.
I have 1GBR and 1Krib in a 20L. At first the GBR was very territorial and chased the krib everywheren but since then the two have apparently become friends. They follow each other all over the tank but I can't say you'll have the same luck as myself.
I had two kribs in the tank at one point and the one was very active and aggressive and the GBR wasn't allowing any of that nonsense. i had to seperate the aggressive krib and after that everything turned out ok.