Emersed plants dying?

[Da Plant Man]

My emerged plants are dying. What could be the cause? Here is what my staurogyne sp. purple looks like.

Notice the browning?

[BIG_Z]

I am relatively new to this so take everything I say with a grain of salt. Some of the plants I have do well for a few month emerged and then seem to just crash (leaves dying and browning for no apparent reason). I flood for a few days and it seems to halt the decline of the tank. No real rhyme or reason to this but it does seem to work. Also temps? Are your emerged setups lit by lights or by sunlight, more sunlight means higher peak temps so sometimes big temp swings.

[kuro]

Most likely fungus/mold, it really hard to see but if you look closely around the plant stem and dirt area you can see shiny strings. The fungus/mold slowly suffocate the plant root and slowly kill the plants. If you were to flood the tank, the mold will dye but usually come back. It really hard to fight it off try some excel or H2O2 in spray bottle and mist the plants.

[salmon]

I'd guess it's a temperature thing, too cold, looks more purplish than brown in the pic...hard to say. Are the stems actually dying right off or just changing color?

[Da Plant Man]

Changing colors. I was thinking too warn, it is lit by lights. I recently gassed it will 100% co2 to kill off some mites. Can't flood it since the soil is too light. Just miracle grow.

I have been growing emerged plants for two years now, and it seems everytime it goes 6 months it crashes.