I have a question about fx5s might be a dumb question ,here goes I have 2 fx5 and would it be bad to run the output of one into the the intake of the other, to make a huge one huge fx5?
Also is there any advantage or disadvantage in this
I have heard of people using an overpowered Eheim in series, with the second unit in the series being unmotorized. I would not suggest doing it for maintenance reasons. It is better to have 2 independent units in case one fails and you'll be able to service the units independently to maintain a thriving biological filter.