I grew Hemianthus Callitrichoides for a long time with great success. I had a 10 gallon tank and 40 watts of CF lighting(T5 would have been better if it was mainstream then). I got a cup of it in that wool, what you have to do really is grab a towel or something and split them up(don't leave the wool, you don't need it). I put them in every cm or so.....they filled in very nicely. They need a pretty nutritive substrate and good lighting coupled with co2. Then you will do well. Then when it's filled in, make sure you keep it trimmed. If it grows over itself the underlayer will die with no light. It also collects algae fairly quickly if your not careful, so keep a close eye on your nutrients.