When using inert substrate-you will need to add ferts of some type. If you have root feeders-root tab and if water column feeders you need water column food. Seachem has a pretty good line of plant food products, however, I have limited personal experience since I don't need them.
You also should schedule water changes so that you add the water column food after a water change-This way you will remove any unneeded/unused food so the algae can't use it....
I would really like to try and keep this thread on the topic of soil based tanks.....