In 5 months your discus should be approaching 5-6" by now. Sounds like they are getting stunted (sorry).
My latest discus juvies have doubled in size from 2" to nearly 4" in 3weeks. They are finally starting to recognize me and come rushing over when I feed them begging for food.
My setup: 4discus 30g long barebottom tank, they have a 55 and an 80g waiting for them as they grow... But for now, 30g is easier to clean. They are a very social fish, so they won't mind the tight spaces until they start pairing.
6x prime reef flakes (50+% protein) - electronic feeder
1x super color (40+% protein) -- in the morning
2x beef heart -- 2 hours before water change
1x blood worm during water change as a distraction
Also, they need ultra clean water for proper growth. So with all that food going through them, 50% water change daily.
Make sure you temp match the water... Ohh almost forgot: discus temp: 85F. Keep them there they are happier, more active, and hungrier. (faster metabolism)
My filters.. G6 & penguin 350 on a 30 gallon. Will remove the g6 soon although I like the combo as they don't generate a lot of water movement but are rated at 150g & 75g respectively. Plus the hob
penguin generates high o2
Lighting is low-medium 10k marine land double bright led
with blue nightlight.
I also just moved them in front of a window (typically a big no-no) but they love the sunlight! Always playing in it?? Wierd. Anyway, with DWC.. No algae has taken hold in a week, so I'm going to leave it and see what happens!