Dual inflow with shared outflow

miki76 · Oct 1, 2026

Hi All, I am building a custom circa 500l / 125 gallon reef tank. It is going to be 70 inch long and only below 20 inch deep.

I want to put two inflow/outflow pipes on opposite corners for maximum flexibility of flow management. I will use a Red Sea reefrun 4000 for each of the inflows.

I would like to have two outflow pipes connected to Red Sea Reefmat 2100 but this of course would require the two pipes to merge before the reefmat.

Has anybody have experience with such setup?
I wonder if the two flows merging could lead to any noise issues or could cause any other problems I should consider upfront?

Thanks for any advice from more experienced reefers!

KrisReef · Oct 1, 2026

No experience with the RS Reefmat, but a quick review of the equipment shows that it has two inlet port on either side. Replacement inlet tubes are sold, so I would wonder if you could use two supplies to the equipment?
(page 11) Inlet hose.
https://g1.redseafish.com/wp-content/uploads/2022/04/8394_ReefMat-Manual_FED_-v22b-1.pdf

Useful_Idiot · Oct 2, 2026

You could merge the 2 drains together for the full siphon before a single gate valve and it would work.

I had my reefmat 1200 plumbed with my display feeding into one side at 400gph and my frag tank into the other reefmat inlet at maybe 100gph. When I would shut off the supply flow into the frag tank with the display still going some times, but not every, the frag tank drain would back up. It seemed the stronger flow pushing straight into the others drain was enough to air lock it. I thought about putting a disk in the middle of the red pipe in the reefmat to deflect flow sideways but didn’t try it.