Hi Jeff,
I'm in love with your big tank - what a great layout and the plant terrace is awesome!
Just a couple of things I wanted to mention - might make life a wee bit easier for you, and better for the discus.
First up, not for the discus, add a couple of teaspoons of salt to the big tank and you won't lose any more fish to ammonia or nitrite poisoning. It's about the only time I ever use salt and it works like a charm.
And for your wee discus, can you up the feedings a bit? I've found that juvies and sub-adults grow out better if they get 5-6 feedings per day. You could use some of Al's fantastic freeze dried blackworms for the extra feedings since you can stick them to the glass and walk away during the day. Then toss in a couple more cubes after your nightly WC so that they get a bedtime snack.
Here's a pic of the cubes stuck to the glass:
I use 3 cubes per feeding for 10 growing discus and they eat them 4 times per day, cuz I don't feed live blackworms. The other 2 feedings are a mix of discus flakes - just about every sort you can think of including beefheart and spirulina flakes.
Mine grow at a rate of about 1 inch per month till they reach 4", then 3/4" till they reach 6", then slow growth for another year till they reach 8". (Females are smaller - only 7")
Hope that helps and keep the updates and pics coming!