I can tell you, you may have some species, such as the fast aggressive growers do well, while another species wanes.

Generally I think it's CO2 related, it's the lion's share of the nutrients planmts compete with eachother for.


Light is the other. From the sounds of it, you have lots of stem plants and likely need to prune often, shading causes leggy growth, not so much intensity of the light unless it's pretty low.

But that will not cause stunting/melted tips either..............

No excess nutrient application will either.
However, too low most certainly will.

As the tank changes through time, does the biomass with all these stems plants
remain the same?


No.


So do you think the nutrient levels also stay the same?
How about the uptake rates?

Do you think 5 cats eats the same rate as 20 cats to maintain the same growth?

No.
Same here.

I see this all the time in marine refugiums where the owner says they have great growth for several weeks, then as the biomass is now huge, the plants all melt.

Basically it ran out of food and exceed the supply from the tank.

Do you think that some plant species might have higher or lower demands for nutrients? CO2?

Certainly.
I've seen Myriophyllum beat up on Rotala when the CO2 was too low, light was high, nutrients where high.

Adding more CO2 solved the Rotala issue pretty quick.


Regards,
Tom Barr