Having followed this link in your profile I am impressed at the capacity and flexability of the system. Heck, after looking up the specs on the aqua controller, I was absolutely drooling at the possibilities, I find myself slightly tempted to buy one for my planted 55 for co2 and lighting control. sure, its an expensive waterchange setup, and not worth it for many people, but for a big tank with big messy fish and/or sensitive fish why not? considering how much we often spend on keeping a $5 fish alive to begin with, whats a little more cash?
and another thing, imagine being able to go on vacation and not having to let the neighbor kid do the water changes to keep your tank alive for another week......