In order to get the same flow rate, it would need to be under pressure, and would have to have valves that you can adjust. It would be easiest with using a manifold and separate lines. I think you might be able to do it using gravity, but it would take a lot of trial and effort. You would still need valves to increase or reduce the flow though.will a main pipe bring the solution to fill all fish tanks equal so that all have the same flow rate?
I would also like to suggest an over flow that bypasses the fish tanks in case the flows to the fish tanks can not keep up . Just a thought.
Jason