thanks,
yea- they were supposed to go where the overflow is now, when I was planning on getting a calfo style overflow tank. not as happy as I wanted to be, but I think it works.. there is a LOT of Portland cement holding them in their current positions.
Amazingly I got those pieces of rock about 6 years ago with the intent of doing this... and never had a tall enough tank to really use them in like this until now...