Opinion:
Sediment should focus on filtration.
Carbon should focus on chemical. Especially chloramine.
As such, your carbon should be the same or larger than sediment.
FYI: I usually run 1 micron sediment, dual 5 micron carbon, 75 GPD RO, triple DI (A/C/Mixed)
Big tank, auto-water-exchange, so lots of water. Plus I tend to over-do things.
I have run 10/10 in the past though, and did not see brown on my carbon, so I really suspect something is wrong.
When you take out sediment filter, look at the ends. Do you see nice indented rings? Or is it mashed, no ring, or offset.
Could simply be a bad filter. Budget brands can be hit and miss.