Hello DataGuru, CS-Gardener, and others,
I do have two Amazon Swordplants (
E. bleheri) in the tank. They were stunted specimens from the old tank when I put them in, but not any longer! I plan to prune them heavily so that they don't take over.
The short, grass-like plants (mostly
E. tenellus) are doing very well, multiplying quite a bit all over the tank. None of the grass stuff is getting more than a couple inches off the ground.
Rotalia macrandra is, indeed, in the tank. It is my favorite red plant. I had this plant in the 50 gal a few years ago and lost it. This time, I'll try harder.
The combined substrate is probably 1.5 to 2 inches deep. For cultivating Amazons and Red Tiger Lotus, I'm not sure that a deeper substrate is better. I think that the reason the substrate went bad in this 50 gal tank is that I had a too deep (2-3") layer of heavy clay garden soil. The Amazon swordplants got severely stunted.
The front unplanted area is only 0.5 inch deep. I don't think it will be a problem to keep clean. I just pour water directly on it when filling the tank, and the debris on top "blows away". I really like having a small, unplanted area.
The thinness of the sand layer doesn't seem to be a problem. The sand and soil have kind of mixed together with many wood particles now on top. It hasn't caused any turbidity.
I did have a problem with the 16 baby Rainbowfish I added to the tank at 2 weeks. They began to die one by one every few days. Suddenly, I'd see one otherwise healthy baby lose its balance and start diving and struggling. Since I bred the fish myself, I was pretty sure they weren't diseased. I didn't think it was ammonia, nitrite, H2S, or lack of oxygen.
So I think it was the wood chips in the soil releasing their organic oils (for example: pine bark releasing tar, creosote, etc, or cedar wood releasing cedar oil, etc). I'd consider these chemicals to be specialized, "oily" allelochemicals (not so much non-specific tannins) designed to protect the tree from disease and pests. It wouldn't surprise me if they caused fish problems in a new tank.
Anyway, I did a 75% water change and added charcoal to the filter (this should help remove the oils and organics that the wood chips are releasing). In next few days, I plan to do another 75% water change and replace the charcoal. If any fish show problems, of course, I'll change water and replace the charcoal sooner. I believe that this will be a temporary problem.
This is a potential problem with new substrates that hobbyists should be aware of....