Lighting up a 25gal - please share experience

[Nordic]

Hi I read lots of things like you need X-watt per gallon, but these rule I also read falls appart on small and large tanks.

I thought a 100l tank is a large, but have learnt it is not, lol

Now the only problem I have with rules like that is that it seems non-sensical, lets say I had 50gal in a upright tank(i know small surface, but hear me out) as opposed to 50 gal in a large wide flat tank, sureley the distance that light has to cover should be taken into account, i.e. 12" or 25" from the substrate.

Anyway, I suppose what works best is to look at what works for the majority of people...

I have the 25 gal with the following flourecent
ZooMed Tropicsun F17T8/5500k/Daylight,
I guess its about 24" long (we use centimeters) It doesnt say how manny watts :< but it seems to do ok, slightly dark in places but I think its because its shorter than the tank.

http://www.plantedtank.net/forum/viewtopic.php?t=3629
Picture there, i removed the stump as it was still turning water very brown, which seems to have triggered some growth in my few poor plants, that pic is about 3 weeks old, have now started dosing Tetra blackwater.

What lighting would you advise for such a setup, (I dont want to have to add CO2 yet, at best will add Hagen CO2).
Also cant realy afford to do anything other than flourecent, preferably in 1 tube as that is all the hood has clamps for even though there is more space.

I am planning to do some Java ferns in there, now that I talked the LFS owner into giving me some from his own tank.

My tank is about 3' wide, 1' front to back and 1,5' deep, 100litres