I have been keeping small aquatanks, as small as 1.5 liters. A few simple tricks that help alot. Look around a little and you will gravel which is also slow release fertilizer. Also, you can buy CO2 pills which slowly release into the water. I use Prodac Fondo Vivo and Prodac CO2 Plant. Both products are really cheap, easy to use, and make your plants happy and healthy. Also, a small tank, such as 1.5 liters, easily fits on a workdesk, under a small lamp with plant light. I have never used water circulation systems in the small tanks, and they are always ok. If you want to consider small tanks with fish, you should browse under nanotanks. There is a lot of good information available for plant and fish combinations. However, tanks with plants only require little care. Tanks with fish require daily maintainence.