The level in the rez is set so that the water level in the bucket is touching or a couple of inches above the bottom of the the inner bucket (the one with the holes drilled in it). The reason for this is I dont like cord roots (the type you see in bubbler bucket grows) to me this is wasting root space.
Here are some pics showing what I mean, these aren't my pics I am only using them to illustrate my point. If you look closely you can see that the roots nearest the bottom of the pot are like cords, this type of root develops when you have a gap between your nutrient level and the pot. I prefer not to have this type of root system as the cords do very little other than support the weight of the roots below.
Here are the roots in a Aquafarm and as you can see they are quite different, this is due to the level being set higher than the pot, and the recirculating nutrient solution. You might notice in the next two pics you can see the water level on the pots. This is the type of root system you should strive for.
I just ran a check to see if Ionic nutes are available in Australia and they are and they are at my hydro shop. I used GH nutes once , the hydro dude actually gave me a bottle of grow free (wanted all the GH gone he said) coz no one buys GH nutes in Australia coz they cost about 3 times more than any of the competitors including Canna who Id rate as top quality.
Finally I feel in sync with you guys as many things available in the USA are hard to get or three times the price here In Aus.