Just out of curiosity are we talking about this "white residue" being more like hard water stains or something...or are we perhaps looking at more like a salt residue/build up from the
nutrients?
If it's the later you could perhaps try using an organic
nutrient instead as I believe the organics won't have any of the salt buildup. I don't use organic nutrients (yet anyways) and you can see I have this buildup around the lid of one of my containers where the nutrient solution gets from time to time.