This is a great book which describes a killifish setup (biotope of sorts) using peat moss as a substrate:
http://www.amazon.com/Complete-Aquarium-Peter-W-Scott/dp/0785770534
I would say, try it. If killifish are the only residents, you are not likely to have anything stirring up the substrate and probably won't have much detritus to clean up either. If you are running only gentle filtration (no powerful HOBs or canister filters blasting water out) then again, it should not really make too much of a mess. Coir fiber could also be used instead of peat.
If you don't like how much it stains the water, run some carbon. If it gets moved around too much (by your hands in the tank, for example) cover it with brown gravel. The worst thing that can happen is that you'll have to remove it and use something else!
http://www.amazon.com/Complete-Aquarium-Peter-W-Scott/dp/0785770534
I would say, try it. If killifish are the only residents, you are not likely to have anything stirring up the substrate and probably won't have much detritus to clean up either. If you are running only gentle filtration (no powerful HOBs or canister filters blasting water out) then again, it should not really make too much of a mess. Coir fiber could also be used instead of peat.
If you don't like how much it stains the water, run some carbon. If it gets moved around too much (by your hands in the tank, for example) cover it with brown gravel. The worst thing that can happen is that you'll have to remove it and use something else!