There are four of them with plans for more.
Unfortunately pics are impossible to get due to the tight nature of the units, I've tried to get pics up in the past and the camera is just too close to get everything in or the flash bounces off the glass. So I can only give you the original plans for now. I probably make a small unit to show how its made, The original aquarist is possibly dead now and I would hate this type of plan to get lost with no-one being able to utilise it Its a bit misleading looking at the plan but what you are looking at is one big tank with 4 tanks built in to it that overflow into pre-filters and on into the individual tanks, the bottom tank is a sump and water is pumped back up to the top and the process starts all over again. hence you only need one heater for each.
Regards
BigC