OC, my 'planted' tank is the 10gal in my signature. It's got FloraMax substrate in it, that's supposedly good for plants.
FreshyFresh - Plants need several different elements to thrive and grow. The plants you mentioned do well in very little light, and your substrate is ideal for them (for those that root). The fish you list in the tank should be providing all the nutrients needed with their waste.
The only thing that may be off is your carbon source.
You've never answered about your filtering (HOB filter, sponge filter driven by air or submerged powerhead, canister, etc). Also, do you use any airstones in the tank? If you are off-gassing your dissolved CO2, this will be a limiting factor in any plants growth. It is by far the most common reason low-light plants do not grow well. If the flitering metihod is off-gassing your CO2, if you can adjust the water return so it does not splash or cause too much surface aggitation, it will help keep the CO2 in the water. Another option is to use a product like Seachem's Flourish Excel. It is a carbon source that is a liquid, not a dissolved gas, so it does not dimminish with the type of filtering.
I've personally kepted java fern, java moss, duckweed, guppy grass and water wisteria (rooted and floating) with nothing but room lighting (nothing over the tank at all) and either no substrate or ordinary 'aquarium gravel' that you can find at any fish store, and those have grown fo rme.
Just trying to help solve the mystery.
I've kept several soil-capped-with-gravel or sand aquariums, both low light and more 'high tech,' so it can be done. In my experience, it can be a bit messy if you like to replant tops of stems, or if you have digging fish. I decided to not use soil for those reasons. It all depends on what you want. I like to grow plants and move them around, replant trimmings, etc. and getting the soil stirred up in the process did not appeal to me.