difference between CF and EC

[EK Holden]

Ron, Is there a difference between CF and EC ? (I am in Australia.Is this a "cross-pacific thing?)
Can this be measured with a multimeter? (If not, then what Can this be a problem (or am I getting
slower growth) by not testing for this?(i do test pH) I seem to get fairly good results for my "special"
crop but want to maximise output for what I can legally grow (~South Australia WOO-HOO . I
like growing in expanded clay balls but am curious ..is it better to leave water constantly circulating
through my system(when lights on)or should it be on/off ? My area is fairly hot and the plants use a
lot of water. (the roots that are coming ut my drainage holes are extremely healthy! Would pieces of
rockwool within the mix allow less watering? How many times can you re-use clay aggregate?

Lots of quetions I know but good information on hydro is hard to find (and your FULL OF IT!!
(and I mean that in the nicest possible way!!) Thanx heaps for any info. EK Holden