Hello Noisey World
I've only tried snorklling on the surface of a swimming pool but could not marster the tecneica of swimming under water but I did learn to stop the mask from steanning up was to spit on the transpart visor + wipe the liqued around with your fingers then just dip the whole mask in the pool. I was taught this my an instutor from the local sub aqua club.
We have a spray gun to put licquad sun tan lotion on smoothly + evenly