Canister outflow

[kennyman]

I was thinking about the canister on sale as Petcetera for my new tank project and wanted to compare it to the Rena  I bought for my cichlid tank. I was surprised to find the flow rate of the Rena xp1 is 250gph rated for only a 40g tank. Vs the 260gph of the Fluval 304 rated for a 70g tank.

Can anyone help me to understand how these canister applications are rated?

[darkdep]

Canisters are really optimized for Biological filtration, not Mechanical.  For Biological applications, a superfast turnover really isn't necessary (or optimal).  It's more about getting water in contact with the most bio media for the longest amount of time.

And the ratings will differ by manufacturer, because as we all know there aren't a lot of hard-and-fast rules in this hobby.

I would imagine that Hagen (Fluval) is a little less conservative compared to Rena.  Hagen seems to be more of a consumer brand, Rena more of a specialist brand.

For Mechanical filtration, you often see people quote 5-10x per hour turnover as optimal.  Canisters just don't do that.

[kennyman]

I got the Rena xp1 to replace a penguin 330. Those high flow hob things are just too noisy for me and did not do a good job at mechanical filtration at all. Not to mention that hob's put unfiltered water through the impeller. That is not a good design no matter what you you slice it. No more running around looking to replace impellers for me!

I figured the canisters would be alot lower volume and much more intensive water treatment. But what I see is the Rena has similar volume to hob styles combined with superior overall filtration. Although the 304 fluval rated for a 70gal vs the Rena xp1 rated at 40gal is still interesting. They have almost identical outflow capacity. I figgure those two units would do the same job.