Petex, your English is far better than my German. My Dad spoke excellent German however. Neither language is easy.
I had some of my CO2 tanks run out today and refilled them.
CO2 was off line for maybe a little under a day, but since I have high light, the response is rapid if there's anything wrong. The Ludwigia "red" had the most noticeable response to this:
I've seen such responses many times as I change CO2 gas tanks often on many aquariums every year. My own tanks can go through a 10lb gas tank in maybe 6-12 weeks. So I chaneg them more often than many folks. Which is to say I can see what happens when there's no CO2 and which of my plants responds negatively.
None of the other plants really cared that much except this Ludwigia.
It's one of the faster growing plants also and right under the light and in the current.
Another plant that responded a little, but not quite as much was the L. sphaerocarpa, but only a couple of tips.
The tips are the key to spotting a CO2 issue.
If another day had gone by without fixing the CO2, other species would have had similar issues or more permanent stunted tips.
These will recover, but would take a bit.
Client tanks that I service once a week can run out of CO2 mid week between the services.
I use to change the tanks before I knew they'd run out, but I added an automated tank switch.
But prior, the tank always had some species that would stunt and had issues.
Since the tank is automated for dosing the ferts, and the water changes are consistent, as the gardening is.......most everything else is CO2 or the feeding routine.
But they do not over feed very often.
Not checking to see if the CO2 gas tank is out of gas or not is a common theme for many hobbyists.
Plants are not growing as well, algae, tip growth issues, curved leaves, BBA here and there, fish being more active than normal during the day, all pretty good indications of poor CO2.
Certain species like the Nesea may takes weeks or even months to recover.
Cuphea is somewhat slow to recover, same with R macrandra and Erio setaceum type 3 etc, they pretty much do not recover the tip, but rather, they send up side shoots that become dominate later on.
Those new shoots can be trimmed a few weeks later and then discard the ratty lower portions with stunted tips.
So each time something goes wrong, it can set back the nice looking garden you spent a lot of labor developing and maintaining.
Many hobbyists get stuck in this cycle and NEVER are able to fully enjoy the gardening and scaping side of the hobby.
Other hobbyist are forced to use only certain species.
Others happen upon some delicate mix that keeps things going okay, but this often fails at some point.
A method should be robust. There will always be folks who cannot pinpoint their issues at some point along the way, but those that keep after it, do eventually enjoy success.
I would try to stick with what other folks have used successfully.
ADA aqua soil, Tropica master grow if you like a brand name, or CMS+B if you like DIY.
These are proven products.
This helps narrow things down more
CMS+B's old recipe included more MgSO4 in the PMDD recipe from the mid 1990's.
But since it's widely used, I use it myself and have for about 10 years, I see nothing I can say that's an issue with it.
CO2/maybe Mg(the most overlooked nutrient I would say), that's where I might work on things. I doubt you are trace limited.
If you increased the traces by 2x or say even 50% more, this should no harm at all. Mg, I have gone up to 25 ppm with touchy plants, and 50 ppm for more robust plant species.
I've never hit an upper bound for trace dosing though. I'm certain it can be done, but I think you would have to go out of your way and not do many water changes etc to do that.
I do not read APC forums, I have not gone there in nearly 4-5 years I guess now.