yea ive seen that on smaller one as well, all though when it is packed with media is set for 500gph ? or the 500gph they rate em at is that empty ? that's my question lol.... im either debating between one of these ac110's or a rena xp4 (used)500 GPH, there is a overflow on the left side of the filter where the intake pipe comes up. if its not flowing that through the filter chamber then water will flow from there. i only see this when the filter needs cleaning.
IMO, I would look into getting a sump for bio and then use the two FX5s for mechanical. It is hard to beat a sump for ease of use once it is set up correctly. In reality, depending on the size sump, you could sell one of the FX5s to cover some or most of the cost difference, and just run one FX5 for mechanical.
Got it, and makes sense. For mechanical I would do the ac 110, for better looks and likely less noise the rena XP4 (or some other canister.) The canister would still give good mechanical, but for the price it would be hard to beat HOB.