At times I wonder if posters who answer posts actually read the OP and try to analyze the OP's problem.
I actualy didn't realy answer to analyze the problem, tried to give some general information i personaly experience with differnet sp of java fern in 3 different tanks at the same time.
There are thousands of combinations which may expose an acute deficiency in one plant and not in others in the same tank.
This is indeed what i fully agree with and makes it very difficult to analyze anything from a close up shot from a few leaves.
And i aslo experience Java doing nothing all of a sudden. (Maybe TS perceives it like that, i do not know.) Everything this plant does, it does to slow to use it as an indicator.. It actualy is a plant that got me scratch me self behind the ears and wonder quite a lot.. had different sp. of it simultaniously in 3 different tanks and the tank i give least of all attention, never fertilize and has no co2 it stayed in rather good health. Also got a bigger low tech in th eliving room with a lot of java ferns where i experienced a lot of die off from older leaves and now does good, but now and then i have to take out a dead leaf, Starts with browning, than yellowing and than lets loose. Actualy a typical sign of potassium/phospate deficientcy, but this i add enough. So it might be indeed co2 deficiency which makes leaves live less longer and grow much smaller. Also grew it fro 2 years in a high tech, it got bigger and much more healthy looking plant. I ran out of co2 about 6 months ago and i reverted the tank back to low tech. And witnessed leaves dying in the same fashion as the pic above shows. Not all and not all of a sudden but in a few months, overall the plant is still healthy.
So having different sp. of this plant in 3 completely different tanks for several years i experience this plant beeing less easy as described and makes you believe and it's also very sp. dependent. I still don't know what to think of it. In the tank i give the least attention and no ferts this plant gives me the least questions.. So i decided to stop wondering and let time take its cause. The plant finaly addapts anyway.
I bought a huge Microsorum Orange, beautyful stunning plant with bright orange leave tips. I planted it to a piece of dw and it started propagating like mad on about each leave it had. Every leave died and i was left with only a number of healthy babies looking simular to about 3 other sp. i have. Since i had so much and little room to keep it all seperate i mixed it up and can't say anymore which is which. The mother completely died in a few months time, not all of a sudden and the babies are still healthy in the same water. beats me.