Welcome to TRT!!
do not think doing a CLS between two systems is possible. keeping the inflows and outflows exact between two systems with one pump, would be difficult if not impossible. are you thinking one pump for both or one pump for both systems?
i think open loops are the only way to do this. do you have a decent sized sump to use for the common area of the two systems? what kind of overflows do you have ont the two systems. what gph can they handle each. the more flow the better for this case. a
super skimmer would help in this. it is better to have all of the water that leaves the tank being filtered by the skimmer. since your temp. regulation equipment will need to be kept in the sump. the more flow the better throught the sump. this will keep the temp drift between each tanks to a minimum.
G~
