As DavidP mentioned, macros just draw nutrients out of the water column. The base of the plants are not roots but what are called holdfasts. They are used to anchor the plants not draw nutrients and water life their cousins that live on land.

Something to consider, depending on your water source and its contents, you can use just plain tap water for your tanks instead of water filtered by a RO/DI unit. The reason alot of people go with RO/DI filters is to combat hair algae problems caused by things in their tap water. Macro algae feed on the same nutrients as hair algae does. Becareful though as Dave said you might end up with a hair algae outbreak as well as a macro algae forest. Besure to airate any tap water that has chlorine in it for 24 hours prior to use. This will remove the chlorine.