I grow this plant in the shaded regions, it's not really a high light plant.
Yes, every other plant can be pearlign and ling and appear healthy whereas one will not.
Ask your self this: do you honestly think that all aquatic plants have the same differential ability to take up CO2? SAme ability to adapt to a wide range of light?
Surface area to volume ratios, KH, physiology, Carbon concetrating abilities, storage, light adaptation, heck, there's more to it than just nutrients, but.........with time, new grow on the side shoots should appear if the CO2 is good, and the light reasonable.
Still, plants do compete with eachother for light and CO2 more than any other nutrient in an aquarium. Sometmes when the N or P is low, perhaps.
Still, I've yet to see one verified Ca++ defiecency for an aquatic plant grow submersed. Plenty of speculation, but there's a lot more to CO2 than the oversimplification we all are sometimes guilty of.
Still, plant species to plant species will have different abilities.
Some are much more resilent and competive than others.
Milfoils, some other species of stem plants are REALLY AGRESSIVE.
Others are more sensitive.
Some take adaption time and then regrow side shoots.
This plant is the later two, it will grow a bit then stunt. After which, if the CO2/light good, it will regrow side shoots and then thereafter there should not be any issues.
R macrandra green does ths, as does the normal red, and the narrow leaf etc.
Many assume all red plants need more light, this was never true.
So there's a few things you can look at. You will not find much if any correlation for Ca.
We can and do routinely add GH booster which is 1/4 CaSO4 and have no issues and have effectively ruled out Ca as a posible issue, whereas CO2 and these other questions are much more difficult to rule out, and thus more likely to be the issue than say B or Ca, or excess K+ and other hokey ideas that have long been shown to be false with these same sensitive plants.
I cannot say what it is 100% of the time, only that which might be likely.
I can say what is NOT, however.
Then you can focus on the other issues that are more likely to bear fruit.
CO2 is always on the table.
If you can change the placement, the current, the light intensity, spread etc, play with more/less water changes, cean filters more often, add Amano shrimp etc you
will find much better control over most things.
Nutrients are perhaps one of the few areas we can simply add non limiting amounts and know there's no chance of a limitation. So that is often why many that use such approaches can conifidently say that a nutrient is not the reason.
It does not imply or say what causes the observation the aquarist suggestsees in their tank, only what it is not.
I've seen the plant do the same thing over the same time frame and know I had good non limiting Ca++.
Later, it did better as the CO2 was tweaked, reduced lighting etc, and just a little patience for it to regrow.
This is not all CO2 is it?
Regards,
Tom Barr