The article you refer to is excellent. However, I do a lot of
etching, have given workshops, and have never found it necessary to
use a fish tank and pump.
I submerge my metal, face down in a plastic tray filled with the
mordant. I like to work outside, on a sunny day, as the warmth
speeds up the action of the etching. I also add some citric acid to
the ferric chloride to beef it up. If you don’t have any citric acid
on hand, just squeeze in some lemon juice.