i was initially taught to use 1:9 dilution of commercial household bleach. after several tries, i modified it to 1:12 dilution.
i usually just sprayed on top of media to get rid of the mold/algae.
leave it there for about 10 minutes and after that RINSE THOROUGHLY (make sure you rinse it enough). that would do the trick.
some orchids dun handle these bleach bath that well from my own observation, bulbos and very young catasetums that just send out their roots. phalenopsis had no problem with this. i had not tried on other orchid genera yet.