Fluval 205 External Filter/cannister Filters..

[The Taffy Apple]

Hi all.. just a quick question on how anyone who has this filter (or any Fluval series or other similiar cannister filter) runs their flow valve.
Obviously, tank size and stocking is taking into consideration and judging by the various videos on Youtube (as does the official Fluval video) the vast majority of people have it fully open, but in relation to the size of your tank what difference is there from having it halfway, fully or even a trickle?

Mine is on full,only ever decreased to slightly below half when doing significant water changes due to splashing my snad substrate. I went by the equation that it should fill my tank 4 times per hour (therefore 'processing' my water volume 4 times every hour), yet i have spoken with keen enthusiasts at work who admit to some very dfferent flows...for instance, one of the older gents with us breeds Discus fish and he believes anything less than full flow wouldn't do the job he needs done. Another workmate swears that he has never run his cannister more than half way, and that's in over 12 years of keeping his tank!

So, can anyone share some light on how flow would affect the nitrogen cycle, be it you have plenty of filtration for your tank or maybe have the very mimimum?

Regards,
Terry.

 

[OldMan47]

Some filter throttling considerations.
If you have a filter that tends to run at too high a flow to maintain a well flooded suction, throttle the return flow a little to keep the suction piping from pulling in air. The size tank vs the filter size is almost meaningless because the volume occupied by filter media is the main thing affecting biological filtration. If you have lots of particulate to remove from your water, higher filter flows may help a little as long as the flow is not high enough to cause suspended materials problems like it did in this tank.

It is never a good idea to throttle flow down to a mere trickle. The problem that creates is simple to state. All impellers impart some energy into the water. The amount of energy is a constant for each impeller. If you restrict flow too much, the energy cannot be readily removed by the flow velocity and is instead seen as heat at the impeller. If the water at the impeller gets too hot, it flashes into steam and becomes a serious problem that damages the impeller itself. A typical safe value for throttling is about 1/4 to 1/3 of the rated full flow of your impeller. Do not try to throttle to smaller values.

 

[The Taffy Apple]

Excellent reply, thank you. So flow rate is not goverened specifically by the size of the tank but what you have in there... makes sense.

Regards,
Terry.