filtering capacity - based only on bio load, or also tank size?

[Brhino]

Let's say you have a 20g tank with 10 neon tetras in it, nothing else, and you've got a AquaClear 50 for a filter. I think everyone would agree that that tank is extremely well filtered, right?

Now let's say you upgrade to a 75 gallon tank, but you don't get any more fish, and you keep the same filter. Normally you'd say that an AC50 won't cut it for a 75 gallon tank, but your stocking load is extremely small. So... are you still okay?

[Cliff]

As long as the aqua clear 50 would cycle the water in the tank 4 times each hour I would say it would be OK. Can't remember there flow rate off hand right now.

IMO you also have to look at flow rate of the filter too.

[Rhaethe]

I believe the AC50 does 200gph, and around 70gph fully throttled.

[Cliff]

I found the manual to the aqua clear 50 (link below), Rhaethe got it right, between 66.6 and 200 GPH flow rate. Presonally, I would want something around the 300 GPH flow rate.

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[Brhino]

so, regardless of the actual bioload, you've got to be able to move all the water. makes sense.