in general not worth it for really small tanks. it is easier to just siphon the detritus yourself then to try and build a skimmer small enough to actually work on a nano system. the problem is that it is very difficult to get a skimmer short enough to work on a nano. the only other option is to make it wider. then the skimmer will take up to much room around the nano to be aesthetically pleasing.

if you feel you must have a skimmer (not necessary on smaller systems) then i would put a sump on the system and put the skimmer there.

G~

 

+1 on ~G

but I built a small skimmer for my 10g tank, but its was tall, and you would still need a sump to use it.

 

I have heard the aquaticlife internal mini skimmer is good, but for a small tank I would just do a weekly waterchange and go skimmerless.