Actually , the leaf size should remain fairly much the same, maybe 10-20% smaller at most once you go to the submersed condition, this is due to less CO2.
A sign or reduced CO2 is progressively smaller and smaller growth at the tips of plants.
Funny, none of those stupid deficiency charts ever mention the signs of CO2 limitations/excesses............and all are based not on aquatic plants, but rather, terrestrial systems where light and CO2 are less variable and generally non limiting........
The DSM tanks I've done have not had reduced leaf sizes of any notable effects...........but I added a lot of CO2 and lowered the light.
As far as EI excess responses:
Years ago I suggested Mega Dosing.
This is where you add 2x the amount typically and then do a water change the following day to reset.
This fattens up the plants, and drives growth much faster than a typical routine might. Then you trim, garden more etc, and then get your photo shoot for the pictures etc. This was often about 2X EI dosing.
This was much more accepted back then, and we knew there was not this horse manure crap often said on line about how bad excess nutrients are, because the group I posted to was a lot more aware that excess does not = algae and we had already done lean methods. The question was more about the plants, not algae or critters. Those are not affected either, but some like to suggest it, or that adding excess nutrients is "wasteful" etc, but we can say this about using CO2 and higher light and these cause a lot more problems and labor issues than nutrients ever could.
But some would rather not address the real issues...........
However, I and others went very high with the nutrients and never found any real upper limits/bounds........certainly none that induced algae, the main question at the time, and fish health and shrimps etc had the same conclusion.........basically it would be very difficult to go to toxic excess levels.
However, waste is still waste, and we simply do not have to go this high for most tanks, rather, start high and then reduce slowly and progressively till you get a negative plant response, then back up to the last prior higher level.
This is how to add just enough using EI.
you are still not limiting growth, but you are not wasting much either as far as nutrients(if you care).
If waste is an issue, then using non CO2 methods, Excel etc and certainly less light should be the focus, because then you use much less CO2/nutrients at the end of the day.
You cannot logically argue for less is more/better while using high light/CO2 enrichment and then suggest less waste for nutrients..........economically and environmentally, you waste much less using less light. This is not a debate, this is a fact.
Stable management of lighting is also far easier and reduces and modifies labor much easier than any nutrient methods.
Sediment based nutrients also waste "less", so using a little water column + sediment sources works even better if this is a goal.
EI is not a large part here, the light, CO2 are, then sediment and/or water column, then there's plant choices, and other factors involved. All these other issues have large impacts on the dosing routines you do/chose.
It's not just about doing nutrients/wasting them.
After the arguments for toxicity for critters and algae blooms due to "excess" fell apart a few years ago, critics have decided to focus on the "waste" and " impact on ecology" aspects.
However, they did not address their own issues with light and CO2 and did not put any of that together. So these too have fallen apart, some simple common sense methods that where suggested all along are clearly there, it's not written in stone and is a myth promoted by folks other than myself.
This method for getting at "just enough" was how I and others arrived at the Trace dosing concentration, it was never with test kits.
This also adds just enough for each unique special tank and system, and does it without a single test kit.
If you look at ADA, they do the same thing, low light(but fools folks into thinking they have more than they think), rich sediments, lean water column ferts(but Amano himself told me to add more and more till the plants looked better, and then when that no longer improved, to stop at that amount, same thing I/others came up with many years prior independently), good CO2 and watching the plants and tank. Then large frequent water changes.
Regards,
Tom Barr