f course, my reason for making the post to start with was to discover the reason for the blackened leaf tips and the suddenly stunted growth. I certainly don't want to repeat this.
I have a suggestion about the spots that you can consider and here is how I came up with it. Almost get the feeling that we were all looking at the problem but did not follow through with what we were seeing. Here is my theory on what the problem is, what caused it, and what to do about it.From msg #18:
Everyone seems so concerned about my use of hydroton. We've been using hydroton for years. Is it really so bad? I've grown in hydroton before and it has never caused my seedlings to stop growing and turn black.
............
Do you guys really think that the blackening of the leaf tips is because of the hydroton? I'm leaning towards a nute burn or nitrogen toxicity. Remember, they were growing well, in the hydroton, until I added 1/4 strength nutes.
I get the feeling that the concern about the hydroton is just because it is not as common of a growing medium as typical dirt/soil or a peat moss or coco coir mixture. You have become used to using it but I figure that most of us are still adapting or getting used to what we are looking at in your photo.
In the first picture we are seeing drop of water on the side of the cup. The surfaces of the hydroton balls are glistening from all the water. If the photo was of a seedling in a cup of soil and that soil was glistening most would have keyed in on too much water right away like we did for the clay balls.
The spots on the leaves have nothing to do with fertilizer or with Nitrogen or with toxicity. Not an issue of too much of any nutrient nor not enough. It is all in too much water on the surface of the immediate area and the use of a plastic 'dome' so as to trap even more water vapor, maybe as a way to promote root growth or maybe something else. But, the dome is contributing to the problem.
The clues are the black spots on the leaves and what looks like the same sort of spots on the hydroton. We were seeing the problem but it was a case of "can't see the forest because of all the trees".
I figure you have one of the most common problems that effects plants all over the world. I figure we are looking at a case of "Black Spot Mold". If we were looking at Maple trees we could call it Fire Blight or if at Roses we could call it simple "Black Spot".
You could panic and toss it or you can make a few changes to make the problem go away and save the seedling. Toss the dome, do not mist the plant or the cup or the hydroton. Just pour what is necessary over the clay balls for the roots. Let it dry out as much as possible but maintain moisture just for the roots. The leaves or any part of the plant above the hydroton line does not need all that water.
When the leaf surface and the hydroton dries out it should be enough to kill off the black spot mold, preventing it from throwing spores and keeping the surface moisture under control should keep it from coming back.
It is what I have done a time or two when I had the same sort of thing show up very early in a seedling stage or when trying to get cuttings to start rooting. Letting the surfaces get dry and the plant recover in the next 7 to 10 days might be all that is needed. If it was me I would wait it out. If after the week to 10 days it was still an issue then I would consider tossing it, doing a bit of sterilizing and trying again.