Depending on where you get discus from, they would do okay with a water change every 2 weeks.
The other thing would be to feed less often, once every 2 days or so to cut down on the nitrate/nitrite and ammonia build up. I would also use gravel as detritus usually sits on top of the sand, but with gravel it will fall through and become less noticeable and plants tend to like gravel more than sand.
your fish selection looks okay as well
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