generally, I don't think there is much point to doing a layered/capped substrate unless you are also dealing with dirt.
I'd say either do the entire tank with what you use as the top substrate, or maybe stick in a ~1" or so layer of MGOCPM, or some other dirt, and then cap with what you like.
Also depends on the tank size. substrate costs for a 10g are bordering on negligible (compared to other costs), while going with premium substrates for a massive tank can be ridiculously expensive...
I'd say either do the entire tank with what you use as the top substrate, or maybe stick in a ~1" or so layer of MGOCPM, or some other dirt, and then cap with what you like.
Also depends on the tank size. substrate costs for a 10g are bordering on negligible (compared to other costs), while going with premium substrates for a massive tank can be ridiculously expensive...