I have a picotope 3gallon (JBL) with this scenerio. I just removed all my saltwater reef inhabitants last week back to my 120g display reef and cleaned the tank really well to start a planted freshie.
So far I have my existing equipment, plus I just setup a DIY co2 2L bottle and bubbles started flowing this AM.
My equipment includes:
9 watts per gallon, wooot! Current USA Satellite fixture with 2 x 18w power compacts and built in moonlight
Rapids Mini Canister Filter w/ charcoal and foam block
DIY co2 2liter bottle with a chop stick stuck in there to diffuse the co2 bubbles... wanting a limestone diffuser or a mini glass diffuser, but can't find any online??!
I added a couple tiny banana plants in there at the moment to get the bacteria flowing.... I'm still waiting on online purchases to arrive, containing eco-complete substrate, HC and some dwarf hair grass.
Realizing the hair grass will go buck wild, I'm going to build small little acrylic "retaining walls" to keep it on the back walls only.
I think I might setup 2 x 2L bottles for co2 and alternate changing the mixture in them every 7 days. I want to post pics so bad but haven't been able to find the power cord for my digi. I'll post em when I find the cord