Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I would skip the humus or peat moss and the sand.
Use pure STS.
STS will remove the KH from the water, and allow the pH to drop. If your fish need blackwater then add peat moss to your filter. You can then change it out as needed.
STS + Peat (I actually used Soil Master Select) is not any better than using pure STS and peat in the filter. And the peat in the filter method allows you to change the amount and add new peat as needed.
Your substrate does not need more CEC, either. STS is already a high CEC material.
If you are raising Killies that breed in peat, then just use pure peat in that tank.