i am not an expert on the various ozone machines so hopefully someone will give you insight into that. as far as your last couple of questions go, ozone is a great overall detoxer so yes i think it would help with candida, as it helps wiht most anything. the ozone in water starts dissipating immediatley and last about 20 minutes. the best thing to do is drink it up right then and there, don;t wait and don't store it. no amount of ozone in water is harmful, however beginners may have a detox reaction to ozone at first. so ozonate the water first for 5 minutes, then 8 then 12 etc. slowly increase the amount of time you ozonate the water. i drink water that has been ozonated for 45 min to 60 min. and it feels great. no meter is needed, i guess you could get one if you really wanted to, but i personally don't see the point. good luck on choosing a machine.