I can see the new stems in the back in the picture. That's a good step in the right direction. (thanks for the pic). Yeah, that's a tall tank. You might try moving the LEDs (if that's what they are) up a little more, just because you want the light coming from above. Er, you'd get more light from a Compact Fluorescent bulbs - they cost around $8, I don't know about the clip-on desk lamps, probably not too much. I think maybe you need more light, but you'll have to watch the plants closely and if they start yellowing or getting leggy, then you'll know. Watts per gallon doesn't work with LEDs or tall tanks. I'm using two 10s on my 10g but maybe you could go hgher than that in terms of watts per bulb and maybe do just one bulb pointed at the middle. Btw, are you using a timer for the lights? Makes things a lot easier, especially the photoperiod. I think you should start with 10 hours and adjust as needed.
The more fast-growers the sooner you'll be done