Since nobody asked, here's how I set up my substrate for a new tank. This is a 20 long I have in the works. Someday I'll get a regular dimension tank, but this is not that day.
Step 1: Worm castings. Lots of nutrients, and high CEC. Lots of organics too, so if you use too much you might be setting yourself up for algae.
Step 2: Activated carbon. You can use the dust, I use pellets as there's less of a chance of it being pulled up by plant roots. Super high CEC, it acts like a sponge soaking up excess nutrients and making them available to plant roots.
Step 3: The nutes. A lot of osmocote+ (too much?) and Mexican red clay for iron.
Step 4: Cover the whole thing in organic potting soil. If I was less lazy I would have sifted out the perlite and bigger chunks of organic matter, but I'm pretty friggin lazy. I also add more Mexican red clay at this point, not only for iron but because it mixes with the soil and makes it heavier, so if you have to pull plants the clay keeps the dirt from being suspended in the water column and it settles way faster.
If I was planning on uprooting plants frequently, I would not be using this method. It does take extra maintenance to clean up dirt around the tank with this method when you uproot things. This section of the tank is going to be dense bushes, so I hopefully won't be uprooting anything.
Step 5: Wet down the soil, making sure it's saturated and fairly compact. You don't want it mixing with the capping substrate.
Step 6: Cap it. I like black diamond blasting sand, but for this tank I'm trying aquasoil because @Xiaozhuang
You can see it's a pretty thick cap (1.5 - 2 inches). You don't want the nutrients rich, high CEC layer to be mixing with the water column too much.
Side question: I'm thinking of just making this a thread for the 20 long, since the lava rock scape is now low-tech (gross, I know). Does anyone know how to edit the title to reflect that?
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