I have corkscrew vallisneria growing in the back of the tank. They have reached the surface and are growing across the top of the tank. Are you supposed to cut them back? There are other plants growing in the center, I think the vals may begin to obstruct their light. Do you cut the vals at the top like with a scissors? Or do you cut the really long ones at the base and wait for new ones to grow? As you can probably tell I'm pretty new to plants. I'm just so happy they are growing so well!