When I'm not working on planning out my next planted tank, I'm thinking about planting other, future tanks.
Last night, I was reading about anaerobic pockets potentially forming in dirt and releasing hydrogen sulfide (H2S) gas. This probably won't be an issue with my next tank (10 gallon dry start with 1 – 2" of Miracle Gro Organic Potting Mix capped with gravel), but given how much dirt I bought over the weekend, it'll definitely be used in larger tanks down the road.
If I were to go with a much thicker layer of MGOPM, would mixing in some seasoned Seachem Matrix help avoid the formation of anaerobic pockets? (This mix would be capped with either sand or gravel afterward.) I'm thinking that 1.) having the Matrix (or whatever) already colonized with nitrifying bacteria would make it more difficult for anaerobes to get a foothold; and 2.) the addition of porous material would help encourage water flow throughout the substrate and further prevent anaerobes from getting too established.
For people who have already tried this, would you mind sharing your results? I'm particularly interested in learning whether or not rooting becomes problematic for plants under these conditions, if you've found a better choice than Matrix (like if seasoned gravel works better and has the added bonus of being cheaper), or if you've used a bacterial supplement like Stability or SafeStart with new gravel/media instead of seasoned, etc. If there's anything you wish you'd known before starting with a mixed substrate like this, I definitely want to hear about it! If you haven't done this before, your comments are, of course, just as appreciated (especially if you see something that gives you cause for concern!).