You can try to cover the foreground with carpet plants. It's a good way to cover up the black substrate.
I'm glad everything worked well for you and this being your first planted discus tank; I'd say good job since everyone seems happy and growing.
They may not be at their full potential but it's still good considering you only feed them twice a day while they're juveniles, ^^.
Also, you won't be disappointed in Mal's FDBW. They're like crack to fish. What size did you order and did you order cube?