CO2, CO2 and CO2 for both.
Bolbitus grows superbly under a very wide range with good CO2.
Java always goes black after it grows well for awhile, and the other plants are also growing well.
Thus the plants increase in biomass.
As they do that, they also demand more nutrients and..........CO2.
So add more CO2.
It'll take a few weeks etc for the Java to bounch back.
I've lowered the CO2 on purpose, never had any BBA, but the fern blackened the Bolbitus rotted.
Then returned the CO2 and the issue went away.
I also tried lowering the light(Removed the MH and left the PC's on), again, the growth returned as there is less growth and CO2 demand with less light.