People will tell you anywhere from 1-2 inches below the pot.. to part of the pot submerged. IMHO it depends on how much bubble action you have going.. with alot of bubbles they will mist the bottom of the pot and the medium will wick moisture.. helping roots seek out the moisture.

You could just put it at 1 inch submerged and then move the level down as the roots appear.

I personally do a 1 inch below because I have tons of bubbles and the hydroton is quite damp with the misting action.

--chris

Thanks for the advice chris, I also have a lot of bubble action. I'll try lowering the water level and see how it works.
What kind of system are you using?

RDWC (Recirculating DWC)
Home made out of pickle buckets..

I'll have to post some pics. But its a copy of
http://www.cch2o.com/index.php?main_page=index&cPath=1_31&zenid=93qgsrf288gbd49go8t5fr4nt1

I sourced the grommets online, used pickle buckets and did an inline pump with sunleaves airpump.

Hope to get some san marzano tomatoes going soon though my heart is in strawberries!

--chris

This is my second grow, but my first using buckets. I'm using three buckets and changing out the nutes for each one. I have two bell peppers and one roma tomato.
I lowered the water level yesterday and the roots are allready coming out of the pots, there were none yesterday.

I would like to see some pics of your setup, the one from the site was nice but expensive! Good idea though.