Return pump ?

[wegotcrabs]

I just bought a 250 gal deep deminsions tank. It has a dual overflow. I currently have a mag 9.5 and mag 12 foamy old tank. I need o buy a pump anyway for my water changing station. Do I buy a new mag 18 and T it off for the returns. Or do I use the pumps I already have and buy a new mag 9.5 for water changing?

[wegotcrabs]

Bump

[rfurst]

You can use two smaller pumps together if you want to. I did this on a 180g using two Mag12's and it worked fine plus then you have built-in redundancy. Depending on how your returns lines are plumbed you can just T the pump outputs together at some point prior to going into your tank.

Not sure what you mean by using a Mag18 and T it off for the returns. Whether you use one or two return pumps you'll want them to reside in the same chamber.

[wegotcrabs]

Yes. Either way it will be in the same chamber. If I use a mag 18 I would plumb the return line to about the middle of the tank and than t off to each return. This way I can try and get the return flow as equal as possible. I like the idea of 2 smaller pumps but I wasn't sure what everyone else's thoughts were.

[rfurst]

sounds like you have a couple viable options, just a matter of preference. either approach will work fine, but yes, using one pump like the Mag18 that you T into both returns will give you more even distribution that using two different pumps into two different return lines.