Cattleya seedlings black patches

[NYCorchidman]

Yeah, that seems more than plenty. I wouldn't mix your tap water with well water.
Rememer, mineral overdose can also burn the plant or at least show toxicity symptoms which are usually quite similar to deficiency symptoms in many crops.

As stated, your cattleya seedlings are diseased by fungal organisms, but suffering calcium deficiency.

[isurus79]

That looks like nothing more than too much moisture with cool temps to me. Its why your mounted plant is doing just fine. I don't think you need do anything except cut your watering back or add a fan.

[My Green Pets]

Thanks dude, that's good to hear, especially since the well is frozen up and I can't get any water out.

I will keep them drier but will stick with the fungicide applications every couple of weeks.

[My Green Pets]

After keeping the plants drier and warmer, plus spraying a bit of fungicide, the black patches seem to have stopped.