External Filters

[Kathryn231]

Please can anyone advise me if I have to place an external filter beneathe my tank or will it run ok if placed next to the tank.
Thanks
Kathryn

 

[markandhisfish]

below the tank is ideal but as the main consideration is that the canister needs to be lower than the intake pipe ( if that makes sense) cannisters are gravity fed ie they rely on the vaccum of the syphon to fill with water which is then returned to the tank by the pump.

 

[rabbut]

Most canisters perform at their best below the tank. Tetratec for example recomend the filter is a minimum of 50cm below the water line for propper operation. Most however will perform provided that they are below the waterline in the tank (Tetratec will work at less than 50cm), but the manufacturers recomend that canisters are placed below the tank as a rule, to prevent abnormal wear and tear on the pump. How this wear and tear occurs, I don't know, but I imagine the manufacturers know something about it that I don't

 

[waterdrop]

Agree, the classic placement of external cannister filters is in the very cabinet that's supporting the tank, either on the floor of that cabinet or on a shelf but still directly beneath the fishtank. If you have a situation where this would be a big problem and it would be much easier to place it on the same surface as the tank, then it might be that you could consider placing it down on a chair seat or other lower surface for the times when its refilling in preparation for being re-primed and re-started. Then after its running again you could raise it up to its home next to the tank, where of course it would need to be some inches below the -surface level- of the tank.

At least I -think- this arrangement would be ok, but it would help if some of the other members would come along and confirm that there wouldn't be other problems with this arrangement. (?)

Two things to keep in mind if you tried this arrangement would be that the hoses would need to be cut to be long enough for the trip down to the chair seat when re-priming and (2) that when doing large water changes you might have to do the same temporary arrangement because otherwise the siphon might stop working near the end of the water change (assuming you were leaving your filter on during the water change.)

~~waterdrop~~

 

[OldMan47]

Welcome to the forum Kathryn.
All pumps have a parameter that must be met to avoid damage to the pump. That parameter is net positive suction head. Pump manufacturers will tell you what the NPSH is for a particular pump and if you try to get away with less, the pump will be damaged by cavitation over a period of time. The NPSH of a canister filter is usually given by the manufacturers in simple terms of minimum distance from the tank's water surface to the top or bottom of the filter. The particular reference point may be different between manufacturers and the minimum height difference between the water level and the filter will also vary by manufacturer. The thing you can be sure of is that if you ignore the recommendations, the filter's impeller will fail much sooner than it should because it will be destroyed by the cavitation. Cavitation is also quite noisy when it is severe which can make you think you have a noisy filter when all you really have is a badly set up filter. Some filters are made to run with the top almost at water level, such as the HOT Magnum by Marineland. Others, like the Rena and Eheim canister filters require quite a large height difference between the water level and the top of the filter. NPSH can be helped a bit by having the shortest practical hose which is why the set up instructions will tell you to position the filter properly then cut the hoses to what they consider the right length to provide for easy maintenance.