Sump for a 125 gallon.
 

What size of a sump is recomended for a 125 gallon?

I'm looking to upgrade and I am new to sumps from canister filters. Any input is appreciated.

canister filters are always rated to a tank size... so that is easy, though always find one rated above your tank. My 125 had an eheim pro3 2080 running on it.

As far as a sump goes, i think the rule of thumb is: as big as you can fit under the tank. I don't think you can over-do a sump. More water the merrier. I would say for that size tank, 30-50 gallon minimum but other than that you could go as large as you want.

Im far from an expert so maybe others will correct this post but thats how i would look at it if i was putting a sump on my 125

Yup, bigger is better IMHO. I've got a 150 gal sump on my 77 gal DT :D

no set rule but 50 percent your main tank is always nice. also keep in mind your baffle height will determine how much water is in the sump also

As said before, the bigger the better! At a minimum, you need enough volume that in the event your return pump shuts off (power failure, pump fail..etc.) that the sump doesn't overflow.