I just installed mine, the water flow feels really weak... kinda sad..

Defective unit?.

the flow will feel weak, but it's not. it puts out a large spread, so the linear flow feels weak.

You are right, the nano is weak. I have one running in a 10g and the ac70 has to be ran on almost full blast to compansate for its low flow.
There is a mod to the nano which removes some of the "gills" which frees up some flow.

If you dose anything, disperse it near the nano and you will see what it does.

I don't have any corals yet, but will one nano be able to keep SPS happy?. The reason being is that I'm planning on installing a hydor flo deflector with a maxi-jet 900, but I know some corals wont get enough flow with that alone.

cut the fins out of the front (but not the ones supporting the prop shaft), and every other fin on the back and you will notice a big difference.

Hm..

Maybe I'll just return the nano and get a koralina 1. Is that overkill for a 14 biocube?

I have a K1 in my 16G bowfront and its weak too. Compared to my K3 and two K4's I was very disappointed. You should see anemones and frilly mushrooms moving around with a K1 in a 16G I would think?
I think I am going to try the new Koralia Evolution Nano 240. Hopefully its an improvement. The bigger ones were awesome except for not working on a wavemaker which they have now addressed with the Evolutions.

try the mod on the nano, you won' be disappointed. I have to keep mine pointed at the surface of the water or my sand blows around.

+1

do you have a picture of this or a link? sounds interesting

Mine is more than enough for my 20 gallons. I would not want it any stronger as I find it already a bit too much. I guess it depend where and how you orient it.

I did not do any mod on mine and it's powerfull enough.