The only thing I'm still working on is a fry proof way to let water
circulater from compartment to compartment.
When I divided a 10 gallon tank into 3 compartments, I siliconed
flexible channels (made to hold sheeting) to the sides and bottom of
the tank to hold polycarbonate dividers. I drilled many very small
holes in the dividers to allow water to flow through (you can stack
the dividers and drill them all at once). I put a small heater and a
tetra double brilliant filter in one end compartment. I then
attached large vinyl tubing over the output of the double brilliant
filter and ran the output to the last compartment. (I notched the
dividers a little for this tubing.) The water would then flow back
through the dividers to the original compartment. It worked quite
well but I prefer individual tanks since I now have a heated fish
room and do not have to worry about heaters in all my tanks.