Pics would be really helpful here mate, if you can try and upload one, without seeing the plant people will just be guessing and may make a wrong call, If it is mold you need to find out what is causing it, Gives the pro's here a headstart buy posting more info
basically as much as you can tell us, lights, feed brand, feed strength, medium, indoor or outdoor, watering schedule, temps of water and res (if you have one), Temps of environment , PH levels.
A picture is worth a thousand words (although when i handed a picture in instead of an essay once, they said it wasn't good enough)