You're kind of asking for the impossible. Most grass like carpet plants are slow growing at best and you have a low light tank. Many people will say it's not possible to do a carpet without high light and CO2 injection, that is not actually true, but patience is the key. This is a subject I've been interested in for a while and have done a bunch of research.

Marsilea, is not grass like but is a good choice for a low light carpet.

Moss can make a nice carpet when attached to mesh squares, flame moss is a little grass like. The moss will need to be trimmed regularly to keep it in carpet form.

Grass like plants:
Dwarf sagittaria, does well with low light but might not be as short as you would like.

Pygmy Chain Sword (Echinodorus tenellus) and Micro Sword (Lilaeopsis brasiliensis) are often said to need high light but there are reports of both growing well for people in low light setups, again growth will not be exactly fast though. I am growing brasiliensis under medium light, no co2 and it is very happy. It actually is growing a little faster than I expected but I had enough plants to split up and spread all over the area I wanted. That is the best method of getting a carpet with most plants but is a PITA to do. Once it gets going you have to trim off some runners if you want it to stay tidy looking.

Dwarf Hairgrass (Eleocharis parvula), makes a lovely lawn effect and has been done in lower light setups but you will find it painfully slow. It will also need trimming to keep it lawn like, rather like mowing your lawn. Nice pic here of Tom Barr's low light dwarf hairgrass carpet:
Dwarf Hairgrass (Eleocharis parvula) - Give it a chance?

In summary a nice carpet in a low light setup is possible but will likely require patience. It's fiddly to setup and you may well be looking at a year or more to get the results you want. Carpets usually requires regular maintenance to keep them looking nice.

 

I find with the grass plants that you need a nice strong light. I routinely killed most of my grass plants until I got my higher light, and what I didnt kill up until that point looked like crap. They easily fell victim to algae, and would look very sparse. That being said the grass plants I have are Blyxa japonica (I killed this without co2 even w/ the better light) chain sword, and dwarf sag. The chain sword throws runners like mad for me.

 

Yea so i went in the fish store today and bought some japanese dwarf rush. It looks pretty cool, hard to anchor down. Iv heard that this plant is known to die off with in a couple of weeks. Is is this true? But I got the store to order me some micro swords. So I'll have some of those soon. Also I have been running my plants with Eco-complete mixed with gravel and putting in Flourish Excel every other day. and haven't had a problem with any of my plants, yet.

 

let us know how it goes.

 

The problem will most likely be your light. The farther the plant is away from the light, the more difficult it is for it to thrive or get what it needs. The plants mentioned may do well in your setup, but who knows. If you had a top grade substrate, since most of them are heavy root feeders, DIY CO2, and dosed with ferts at least once weekly, you'd increase your odds of success with that light. You may not need all of that, but supplemental CO2 has been proven to take a plant that requires higher light levels and do just as well in much lower levels.

A plant needs lighting, fertilization, good substrate, and CO2. If you lack one area usually a plant can adapt to your tank. Take away two and the plant will usually not do well. Generally speaking.