That's the point I'm trying to make Tom. Never did I recommend not adding ferts to the water column and using only tabs.
I'm not saying adding any ferts
to the water column.
I'm talking about non limiting conditions
in the water column for all nutrients
all the time, that's quite different than just adding say some Traces and K+... vs adding....... KNO3, KH2PO4, Traces, GH etc.
Many that add root tabs etc, already add other things to their water column such as traces(some once a week, some daily, some 2-3x a week), and without adding KNO3, obviously adding a root tab with KNO3 will help in such cases.
There have been times in my tanks when I did not have root tabs and there have been times when I did. My dosing routine, lights, Co2, etc. have been unchanged since just after starting the tanks.
And what happens, since as you say, things are unchanged, to the plant biomass? Is it growing and increasing, or does it always stay stable?
Most tank's increase in their plant biomass after you start them. As they grow, the dosing needs to be increased to maintain the same unchanged levels.
When I use the tabs I've noticed a better root structure and faster reproduction of some plants. Not all, but some. In my opinion that is worth the $7-8 I might spend on a pack of tabs that last me over a year. I'm sold on the fact that Amazon Sword, HC and Giant Hairgrass grow nicer and faster for me when I use the tabs. Does that mean I should dose more into my water column and stop the tabs? Maybe.
This is your best arguement for a richer substrate.
Stick with this.
You can argue having a nice back up for nutrients if you are no good with water column ferts and are not as consistent etc with it.
You can also effective argue less transport issues when you have nutrients in both locations.
But I'm set in my dosing routine, I have ZERO algae problems and I'm happy with the way things have been going in my tanks. Why screw with it and possibly cause an algae outbreak.
To test to see if your notions are correct or not.
To learn another method.
To have more methods available to you so you can better understand and manage things.
I have zero algae issues with pure water column dosing also, did this for about 10 years on many tanks.
The hairgrass I grew was nicer than anyone's.
Swords more massive and downright weedy.
We did not have HC back then.
I'm just the type that would rather spend more time enjoying my tanks than screwing with them or changing things. I stick with what works for me.
Nothing wrong with that, since this is your goal, I should suggest you try a non CO2 approach and reduced lighting.
These are better ways to reduce issues and provides more wiggle room for a method.
Knowing what trade offs each method affords is useful.
As for the brand of tabs, I prefer the Seachem tabs because they hold together until they are completely used up. You could pull what's left of it out of the substrate after a month or two and it will stay in one solid piece. The aquariumplants.com tabs do not hold together well and will disintegrate all over your tank if you disturb them before they are gone.
I like the SeaChem version also, but adding a macro nutrient will help as well to the substrate.
The cost of a bag of soil? 2.99$.
So you are actually somewhere in the middle, wanting to deal with some trade offs, as will someone wanting faster growth using CO2/more light, water column ferts as well.
As far as Seachem tabs causing algae, that's hogwash, as far as adding traces to the water column causing algae, again, hogwash.
I should have had bad cases of algae on many tanks over many years if any of that were true.
Same with NO3 and PO4 for that matter.