I was doing some research on dwarf gouramis (and I almost bought some for my tank... I decided not to, because I couldn't find any females for sale in my area and I wanted 1 m and 2 f.) In my research, I read that dwarf gouramis are particularly prone to parasites which can show up as ridges, ripples or bumps on its side. I also saw many sites that recommended quarentineing them for 3 weeks after purchase and treating them for parasites... maybe that's your fish's problem?