Thanks for your to the point reply.
It sounds like you could offer some details regarding the function and use of various humates and their use and benefits in the aquarium. I am trying to learn.
Experience(decades) trumps speculation?
Adding to that, a copy of Steinberg's Ecology of Humic substances in Freshwaters: specifically Ch 6,7 and 8.
What do you think produces said humic substances? Plants.
Plants cannot run away, move around etc, they have to deal with what is there. Humics are common in aquatic submersed systems. The Santa Fe River in FL is an extremely rich Humic system and it is full of aquatic plants.
Same with the lower Suwanee Refuge, most of the Everglades.
Natural/lakes/river studies do not support closed aquarium systems however.
But as Hobbyists, we have a long history of using peat for plants and fish.
I've used it for maybe 20 years?
the other issue is that no one really has any idea at what concentration the HS(Humic substances) are nor what type, but we can know a bit by using the same source material for HS, eg, pear moss. Driftwoods leach considerable HS as well.
Need a control? add Activated Carbon.
Water changes can be done also, but add different issues to plant growth etc.
These things can be done by aquarist (and have) over many years.
I see no evidence that they are detrimental other than aesthetics of pee colored water.
Steinberg's table 8.9 and 8.10 do not detail the various researcher's experimental methods, clearly they are NOT all the same and the depth and other factors come into play. He states that the evidence is circumstantial.
There is other discussion in the text as well.
Without knowing specifics about the HS in question and that we use, it's a bit tough to relate that information to our aquariums.
But............if a company is selling something, they will misuse such information in most cases to get your money in this hobby.
That is also something learned over time and based on a lot of experience also
Stick with good old peat moss. Driftwood etc.
It sounds like these acids do to trace metals what every acid does: lower the pH. Doing this makes metals more available in the water column. Put HCL on a spot of ferric oxide (rust) What happens? It dissolves the iron and makes it possible to clean the rust.
Lower tank pH's will "dissolve" metals. I'm not saying that these things don't actually bind to the metals and make it easier for them to cross cell walls, but for that to happen there needs to be iron in the water column to begin with.
They do have some ligand complexing properties. Pages 245-256. This prevents uptake for fish/inverts of metals across their gills. Basically longer lived but lower toxicities. This is good for plants and metal requirements.
So the Humics can be both good and bad for different organism. A little is good, a lot of anything tends to be bad if I were to guess. So driftwood, plants etc= good, yellow water= not pretty, but not a problem either.
Plants really do not seem to care that much, but it's not an aesthetic most like.
So it's unlikely to be an issue for most planted hobbyist and the nuggets and all the other items Vendors sell you? They are only going to sell something pretty watered down. As many hobbyists find great ways to over dose and lard things on..........
So, save your $. By a sack of Peat if you wish.