Easy Plants For Freshwater Aquarium

Java Moss won't carpet the bottom, whatever substrate you have. It needs solid objects to attach to. In any case, on the bottom of a tank it will grow quite tall and lanky, towards the light, not make a low carpet. You can get stainless steel mesh to which you can attach moss, which works quite well You just attach the moss, then put the mesh on the substrate. Several pieces of mesh spaced out over the bottom of the tank can look quite effective. There are other mosses that stay shorter and more compact than Java moss, but they are slower growing, harder to find, and more expensive. EBay is as good a place as any to find them. You can also attach moss to stones, either by tying with thread or using superglue (see threads on this forum re superglue). You could also try Riccia, which is actually a liverwort rather than a moss and needs good light, but can look nice.

Plants can be grown in pots, but they would probably have to be bigger pots than the ones that plants come in. You would also need to add root tabs to provide them with the nutrients they need. Wood with Java Fern and Anubias attached is probably the easiest option, but being slow growing I'm not sure they have much effect on nitrates. The best nitrate reducers are fast growing floating plants such as Amazonian Frogbit.

Hygrophila polysperma is a stem plant that grows like buggery (technical term) and uses lots of nitrates... in fact, all the Hygrophila that I've tried are easy growers and will root quite easily in any of the various sand and gravels that I've tried.