Clay gravels like Flourite provide oxidized minerals, mostly iron
Eco-Complete has no nutrients. It has room for the storage of nutrients, though.
That is not true at all. How do you come to that conclusion. It provides several minerals and has a guaranteed analysis right on the bag.
There are two type of nutrients plants use. Macro nutrients and minor nutrients. Minor nutrients are minerals. Macros are nitrogen, phosphate, potassium, calcium, magnesium... Clay or rock substrates only provide minerals, but they are inert and last forever. Roottabs, depending on who makes them usually contain some of both, but degrad, dissolve after a couple months or so.
Soils contain a mixure of organic and inorganic material, and may provide both macro and minor nutrients. Organic matter of any kind decomposes at some point unlike a mineral substrate.
but roots do not love the texture as much as dirt, and it does not seem to use the fish waste in as good of a way as soil does.
Actually fish waste can help to turn the oxidized minerals found in clay gravels into the more readily used water soluble form. Iron for example. If you remember high school chemistry, the oxidized form of iron is Fe+3 the water soluble. chealted form is Fe+2. Plants use Fe+2 much quicker. The same thing happens using soil. Organic acids as well as fish waste act as a chealator.
These companies just make a killing on people just getting into live plants(I was one of those people) only for them to learn they need put root tabs in every couple months.
I have used Flourite and Eco complete for over ten years. I am no newbie! If you know what nutrients any substrate, including soils, provides for plants, then you know what else to add. Whats missing. Its not that difficult.