I have kept and bred M. boesmani and they developed this so called fungus around the mouth area in my early days of maintaining them, I was advised by an old aquarist friend that a little bit of cooking salt added to their tank water coupled with a higher pH 8.0 - 8.5 would soon eliviate the problem. Lo and Behold he was right, the fungus or white substance cleared up within a mater of days and the fish looked much more colourful, healthy and vibrant.
Regards
BigC