I would get some wood in there and attatch some Anubias and Java Fern. If you had a branch then you could attatch Moss to it and let it grow along it. I would add some Crypts to the foreground and then some stems such as Cabomba and Elodea towards the back. Some Vallis for the background will also fill it up rather nicely too. Use Anubias Barteri Barteri for mid-ground and add Barteri Nana for the foreground.
I think my silver dollars and some of the other fish will eat the plants though or won't they?? I might just go with artificial ones and change the substrate to sand, also when using sand does it ruin the filters??
java ferns have a bitter taste not much eat's them... you'v be safe with them... as for ferts you wouldn't need them with Java's there fairly undemanding plants
I wouldn't have said that your tank is big enough for Silver Dollars?
When changing to sand you will need to wash thoroughly so it removes any dust and also the lighter particles that will cloud your tank. Once rinsed thoroughly it should be fine, especially if you take care when adding water so it doesn't disturb it too much. Try pouring water onto an up turned plate. I also rinse the filters motors and media after a few days as it can wreck your motors and impeller if left.
with sand couldn't you just put your filter in a bucket and dose ammonia (with no fish ofc) while it settled.. or move it all to another tank / bucket? or large container? keep the whole set up going? while u changed it
To change the substrate it would only take a few hours so wouldn't need to be fed as long as it was kept moist. The fish are also fine in a bucket with no heater or filter for this length of time.
Mine was crystal within 24 hours the first time i used play sand, the second time it was clear within about 4. (admitadley with a better filter) When using unipac sand it was clear within a hour.