I am using two Eheim 2228 Pros that I already had, as pre-filters, to drive the reactors. The media trays are filled as follows:
Bottom: Eheim "coarse" sponge with denitrate on top
Middle: Eheim "fine" sponge with denitrate on top
Top: denitrate with Eheim "fine" sponge on top
Each 2228 "pre-filter" is running at approximately 30 gph. The 2228 pre-filter on my 20 gal is, itself, pre-filtered (the intake hose is inserted into an uplift tube on my UGF). I haven't yet determined what, if any, additional pre-filtering I'll do for the 2228 on my 265 gal.
The reactors I have are the NextReef MR1 and the NextReef MR1 "Monster". I did not have the best shopping experience with the e-tailer I used, so, I am reluctant to tell you the e-tailers' name. You would be best off to google on "nextreef" and go from there. I got a great price on each of them. The MR1 was $69 and the MR1 Monster was $143. The Monster was $30 cheaper than what Marine Depot charges!!! MR1 was significantly cheaper too, but, I don't remember by how much.
Again, I got a great price, but, I can't (in good conscience) recommend this vendor. If you are getting ready to order from an e-tailer you've never used before, I HIGHLY RECOMMEND that you check out their reseller ratings first!!! I was fortunate that, by the end of my journey, I received everything I ordered, but, it was one of the most least comfortable online shopping experiences I've had in a long, long time!!! In fairness, the e-tailer stepped up and addressed any inconsistency(ies) with my order, but, I never need to count on heroics and pray for integrity when I shop at somewhere such as Big Als or ThatPetPlace. Overall, it was twenty days until the reception of this order was fully complete!!! RESELLER RATINGS!!! USE THEM!!!