Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Depending on how good the reflectors are your tank is right at the edge of using or not using carbon.
The easiest to use is probably a liquid source such as Seachem Excel.
The smallest pressurized set up would probably work, such as paintball or a similar sized set up.
An easy DIY system using yeast and sugar would work for that size tank.
RO is more for the fish. Fish from soft water habitats would have problems with GH over about 9 German degrees of hardness, and most would prefer GH under about 5 degrees.
There are plenty of fish that would work in your tank that come from harder water, so unless you are set on one or more of the soft water species, I would go with what you have, and not get into the complexity of trying to alter your water.
If you like trying such things, though, and can get the RO unit at a good price, it can be interesting. It really is not that difficult.