I found this easy DIY substance
Cheap Sand-based CO2 Generating Sub
Here's a recipe I've been using for 4-5yrs for a low cost, long life substrate that suits just about everything I've grown.
Propagating Sand (Bunnings $4.95 a bag)
Marble Chips/Oyster Shells
Blood & Bone
Laterite (optional, as the sand has a lot of clay in it)
Peat Moss (optional)
Cover the base with 1-1.5cm unwashed propagating sand - straight from bag, heaps of clay
Sprinkle marble chips - 1 x handful per 30cm square
Sprinkle blood & bone - 1 x dessert spoonful per 30cm sq
Sprinkle laterite - 1/2 x handful per 30cm sq or lay cut and dried potters clay
Cover the lot with 3-4cm well washed propagating sand, don't want all that clay in the water column!
Cover with cling wrap and fill to desired level to work with plants.
The propagating sand is full of minerals and a fair bit of clay... that's why you can get away without using laterite. Coupled with the B&B for N & Ca, the gross feeding plants love it.
The marble chips help maintain ph balance, which is needed for efficient nutrient uptake, and provide an ongoing Ca source. It also acts as the carbon reserve, supplying CO2 as it dissolves. Oyster and other mollusk shells do the same and are the building blocks of aragonite.
The sand is fine grained for a substrate, which keeps all the **** from leaching into the water column. But it really encourages micro-organisms, worms, etc... and I find that the spiral (Malaysian) snails keep it really well aerated - not to mention the Corys rooting around.
In three years I've never had a problem with fouling or gas build up.
I've tried adding a fine layer of peat, but haven't noticed an appreciable difference either way.
The substrate in my shrimp tank is full of tubifex, which aerate it constantly and transfer nutrients up and down through it. My CRS/CBS seem to love the free treats they deliver.
Give it a go - even in an experimental tank.