Lets go over some things first.
Lets talk about lighting.
What lighting do you have ? Or what watt bulb(s) are you using?
This will determine which plants you will want. The more watts of light the better.
Make sure you have not too high nitrates. This can cause some unwanted algae to grow on the plants.
The gunk, is dietrus and leftover food ect. that ends up in the gravel. You do want to get this out.
When I started to add a few Amazon Swords to my one tank, I wondered about Vacuuming as well. To my surprise, I didn't need to vaccum near the plants. They started to use it, the gunk. I did keep vaccuming, where the plants were not. SO when the roots start to adsorb what is in the gravel, you will need to vaccum less.
You may want to add some basic liquid supplement, and possably some plant tabs with iron once you decide what plants you want.
Hope that helps for now.
