I have no idea what a recirc system would do with hydroton, but I use it for an ebb and flow table that I just put together.
I have done 5g bubbling bucket systems, top drip "bubbleponic" aka dwc with a drip systems, and aeroflow systems, but this is my first ebb and flow system. I have always used hydroton for the stability feature and not to hold water like the rw cubes, or soil.
My setup for e/f is a 3x3 tray with two 600w lights in 6" glass tubes (one digital one magnetic(magnetic is still brighter)) spaced 2' apart with mylar drapes on 2 sides and an 8" fan for cooling. I use a square fan on one side to push the canopy air through the funnel. I am taking pictures as it goes along, but don't want to post any until:
1) the clones take
2) until I am comfortable with this forum
My setup for the tray is 6" rw cubes for the clones, and hydroton filling the void between the cubes up to the level of the top of the overflow drain.
I fill the tray up to the top of the overflow valve on the tray to keep the water from being exposed to light, and also to trap moisture for my soon to be root mat. The hydroton is totally exposed but since it doesn't wick, and the rw cubes don't either; I haven't had to worry about mold on the surface unless I spill on the top of the cubes. When that happens I will deal with it, but it shouldn't be a problem.
My flood schedule is as follows (not sure if it is proper but it works for now):
3min when the light turn on
3min half way between on and off
3min.... 30min before the lights turn off
I do this because the tray is 6" deep and I want to keep the moisture in without adding light to the water which (i was told) will produce mold. I have heard that 1.5min is sufficient and I would love to dial it down, but I know what over watering looks like and would like to use that as a benchmark for my adjustments.
For nutrients I use
GH flora series, liquid kool bloom and Advanced Nute
Bud candy. I have used it in the past and have had great results so I will stick to it for now.
My use of hydroton is strictly to keep the light off of the water and provide a surface that is quick drying and with depth that will lock in the moisture which is left in the root mass. From my experience it is a poor conductor of heat so I am hoping it wont bring heat and/or mildew to the root mat. My main use for it is so that the roots can grow around it and encompass for stability. I could be wrong but my experience tells me that hydroton doesn't hold in much moisture.
Just my take on it... I would love to hear more info from the pro's, but I hope it helped!