Daghan man maka influence sa growth speed sa plants... Having a good light source is one, pro you also need a good source of CO2. and nutrients sa water column (Fertilizers)... Since imu tanks is 2.5 gals. I think your light is enough. You might have to look at your CO2 levels. Ga excel ka dba? that would help. But remember HCs are naturally slow plants, and would really take time para mo adjust. If nahan ka upgrade sa CO2 tank, mas maayo... Also get ferts, gamay2x lang dose kay gamay man ka tank... i think nahan sad ni cya medyo bugnaw na water 20-26... dli ko sure...
Now to answer your Q? Nag DIY ko na LED lamps...I used 3W GES MR16 LED Lights, Wide angle, Day Light... 16 pcs... 300+ per piece and ako cya gi install sa built in hood sa ako tank. Mahal japon, hehehe pro mas nahan ko kay i am able to use my hood... Pro if i didn't have the built in hood sa ako tank i would have bought the zetlight sa pipers...

Check sa aquamagic naa na cla cheaper brands sa Led lights if nahan jud ka mag led...