For dwarf baby tears you need high light for it to grow and carpet at it's best. A 20L is shallow so you might be able to do a 2 bulb T5HO fixture. I would put 1-6700K bulb and 1-10000K bulb. Dwarf baby tears will do best with CO2 but is the one carpeting plant that will do well (just fill in a bit slower) with either Excel, Glutaraldehyde, or API CO2 Booster. I use Glutaraldehyde, which costs me about $27 for 2-1/2 gallons. It's very economical to use. I run a high light, heavily planted tank and only use Glut. You can see the growth I get for yourself if your interested....
http://www.aquariumadvice.com/forums/f70/220g-planted-newly-rescaped-231568.html.
Here is the info on the Glut...
Glutaraldehyde is a liquid carbon and is the same as Excel, even smells identical to it. I have never had any losses, fish, shrimp, snails and I use a higher than normal dose (which if you read the excel bottle says you can increase dosage slowly in high growth tanks) and I've used it for quite a long time. Used to use Excel but when I got the info on mixing Glut and RO to get an equalivant dose to Excel I haven't looked back. Glut is 2.6x stronger than Excel so I get this...
Glutaraldehyde Cold Sterilization Solution 14 day 1 Gallon: Amazon.com: Industrial & Scientific and mix this one gallon of Glut to 1-1/2 gallons of RO water to get 2-1/2 gallons of Glut for $27 dollars. Look up how much Excel would be for 2-1/2 gallons. I dose 1ml per 5 gallon(due to my high light and plant load) but you would need to dose 1ml per 10 gallons. It's never melted anything, not even the Corkscrew Val. Also these products, Excel, API CO2 Booster, and Glut all breakdown in the aquarium in the range of 11 to 24 hours depending on what research you use. That is why you use it daily.
I would carpet the front of the tank but also add some other plants to the back of the tank, especially if you are going to go higher light. Some good ones for that size tank would be water sprite (fast grower and uses alot of excess nutrients in the water) as it grows quickly and is easy to trim to desired height and shape. A couple Crypt Wendtii Red or Bronze to add a non-green color. Some Telanthera Rosefolia (Alternanthera reineckii) and some Myriophyllum tuberculatum to add some color. The Alternanthera has bronzey green upper leaves and hot pink under leaves. The Tuberculatum is an orangey color with more dark red orange new growth in bright tanks. Also these plants will give you different leaf texture and shape along with some color.