Besides growing huge, the loach is a social fish and they are best kept in groups of three. I am deffinately NOT suggesting another one. I AM, however, suggesting you re-home it sooner as it deserves the best quality life possible and alone in a small tank is deffinately not that.
If the tank is the 20 gallon in your signature I'd say it's just about ok but don't add any more fish and take the loach out.
