Well by connecting them all I really need is a new light. If i run it separately then it is a different story. Plus, by connecting them I can be sure that both systems have the same parameters and that I can do a WC on 1 only instead of two.I guess my question is, is it worth the hassle or the potential consequences if something goes wrong? Might be easier just to run them as two separate tanks, considering you don't want to buy a return pump or drill either tank. What benefits are you specifically hoping to gain by connecting them?
By the looks of the replies here, it could work, the only problem is that if something goes wrong, the frag tank will flood.