advices for ray for "newbie"

[thanantosis]

hi al bros!

been away for more then 7 years.
used to be here often when a RTG is cost 400 plus and a ST cost 25 sg

used to kept a few motoro and some hybr those days with my arowana, st, ff, endi etc

i wanted to get back into this hobby once again and needed some advices

im moving to a new place soon. and have a small pond. about 3ftx16ft.

but only 30cm water depth. filter will be external filled with 5kg biohome.

whats your advice on this for rays? number of them? or is this tank even suitable?

ps: shock to see its so quiet in arofanatics... used to be a busy place

thanks alot bro!