kudos on the unique tank! you've got great ideas.
they usually hide when scared. their obviously very happy in this tank because he provided a very good home for them. i hate when people come to my work and buy them and try to put them in like a 10 gallon tank with blue gravel and all that jazz.
I did my homework for quite a while before I even started to design this tank. Even after the build, I waited a couple months before adding the eels.