since both you and mpl have asked media questions i'll tackle that question first.
there are two techniques for watering.
one is the full flood. this is fully flooding the plant container and then fully draining it. similar to e&f but flooding from the top and draining from the bottom. it achieves a 100% gas displacement. it is techncally harder to do as it requires a larger pump and a larger reservoir and bigger plumbing so that you can deliver the solution in a very short period of time in sufficient volume to overwhelm the drain capability.
it also requires a medium that won't float such as turface or pumice stone. i think fine lava rock could be used also. i don't know if the growstones float or not.
the main advantage of this method is that it takes the guesswork and trial and error out of the equation. full is full. you can see it.
the second technique is a frequent but intermittent pulse of sufficient volume and frequency to keep the medium wet but not saturated.
this is much easier to do technically and grows the same size plants but you must work and think a little more about the requirements of your choice of medium.
pure perlite has to be irrigated about every 15-20 minutes. turface once per hour or so. pure coco once per 3 hours and so on.
with my 50/50 coco/perlite mix i'm finding 1.5-2 hours to be about right.
with this device we are watering the medium not the plant. trying to keep it in that ideal band.
i have used perlite, coco, turface, which is a calcined (kiln fired) clay like hydroton but vastly superior as it won't float and has much greater water retention and release. it will hold it's own weight in water, also i have used rice hulls but really they function exactly like perlite. pumice stone, which is real good stuff but may not be readily available in your area. i have used diatomaceous earth in the form of auto parts stores oil spill clean up stuff. if you can get the right grade it works good. i liked the napa auto parts product #8822.
we have at least one grower here using straight hydroton with the pulse method.
i have used combinations of almost everything listed in various percentages.
i am currently using a 50/50 coco/perlite mixture for several reasons. as we have scaled up we found turface, de, and pumice to be labor intensive to prepare. it's all good stuff for smaller grows if you only have to clean small amounts but with larger, multiple room grows with lots of large plants we would just about have to hire a full time employee to do nothing but clean it.
also not all of these materials are available everywhere. they can be hard to source.
but coco and perlite are ubiquitous. and very easy to prep. the coco is ready to go right out of the bag if you use a high grade loose fill type, like atami or roots organic's coco palm. the only thing we do to it is give it a 1 hour soak in an ec 3-4 calcium nitrate bath to satisfy the cec.
perlite is easily cleaned by just floating it in a large tub, stirring with a boat paddle for 15 minutes and skimming the good stuff off the top after the fines sink.
perlite has no cec but coco is about 70 meq/l. turface 30-40. pumice slightly less than that. de probably a little greater than turface.
all of these choices have some capillary rise capability and you want at least 6" in this device. coco has the greatest again followed by turface and de and then pumice followed by perlite. pure hydroton has very little and, while it works well in the drain i feel you are gambling if the power goes out. large plants can dry out fast and the ability to sub-irrigate can save your crop.
also i think a good capillary rise capability grows a bigger plant by guaranteeing the availability of water and nutrients 24/7.
at work ^^^
