Interesting. What are all the different plants you have in the super rich substrate?
Rich but otherwise "balanced" though?
I wonder what the result would be if the substrate contained very high amounts of a particular thing? I'm pretty confused by all the toxicity conversations bouncing around everywhere...
All the usual suspects (my stunting gallery) - a couple of varieties of wallichii, a half dozen varieties of macrandra, Ammannia gracilis, senegalensis, crassicaulis, and a couple of varieties of pedicellata. Rotala Sunset. AR Mini, AR Variegated. And a few odd plants that I didn't have room for elsewhere.
I wouldn't call the tank balanced by any means. But certainly very well-fed once the plants send out roots. This tank could go a couple of years without water column feeding.
Trace toxicity believers are always present in the fringes. They seem to be an anti-social and tactless bunch, possibly because they feel they have the solution and nobody wants to listen to those ideas. They're not wrong. If you grow Lythraceae and dose all your ferts exclusively thru the water column and you have old Aquasoil or inert gravel, you too would become convinced that trace toxicity is real.
I've not been able to consistently grow Ammannia without stunting using water column dosing, regardless of KH or CO2 levels. But I have been able to grow Ammannia under poor CO2 and hard water - CONSISTENTLY - if I root fed them. But for the sake or argument, let's assume I have poor husbandry skills. How do you explain Burr's experience with Ammannia? His maintenance and husbandry skills are about as good as they get (just look at his award-winning tanks!). But he cannot grow Ammannia consistently despite flawless husbandry and high CO2. But he also doses his water column as the primary source of plant food.
Most Ammannia species are reluctant aquarium plants and I am of the belief that they are much better at nutrient selectivity through their roots and terrible at it if you leaf-feed them. You can get by with leaf feeding, but the stars have to align and you have to know what you are doing. Whereas any idiot (see example above) can grow them if relying exclusively on fresh aquasoil or O+ or root tabs.
In my experience 95% of plants are thrilled with high water column feeding or call it EI. But EI causes hobbyist fatigue - you gotta clean, do big water changes, cut and trim and vacuum and on and on. It's work to keep up with rapidly growing plants. And if you screw up, algae shows up in a hurry. If you don't have time or are lazy, consider quarter-to-third-strength EI. This is a great compromise.
But plants like Ludwigia, Blyxa, and most other plants thrive under full EI. The other 5% of plants have issues under EI.
The Ghori method - about one-third strength EI (13-1.5-13 nitrate-phosphate-potassium respectively, per week) plus Seachem Flourish Comp and Iron for traces is a great compromise between touchy Rotalas and greedy Ludwigia. Most people I've directed to this method are happy with their Rotala.