I use an FX5 and a 150g rated wet/dry on a 210g. I like major current for my Retroculus X. and plecos from swift warm water rivers (Tapajos & Xingu). I chimed in because I like the biological but love the option of using Purigen, or any other media to remove whatever comes up. Recently I needed to treat with Cupramine and you have to remove it with Cuprasorb before you can do a water change and use any water conditioner (reducing agent) or the copper spikes and kills everything. So, use one for each, there's plenty of media trays to use what you want. I have a similar set up on a 300g, FX6 & 300g wet/dry...same reason current and over filtration for X-Lrg L14's and a 14" Tigrinus cat. I like having a sump so I can run a sponge filter in case I need a quick quarantine tank, or the usual reason...More Fish! Side note, and maybe someone better educated can answer, the gph on the FX filters is fast, I'm not sure the how efficient the biological process is in such quick turnover.