Your post and photos

Can't really tell much from the photo. I suppose infected seed is a possibility but I would have expected to see signs of it long before now. And some nutrient deficiencies can mimic this too.

But it does look like that one leaf on the left side of the picture "seems" to have a bad infestation of aphids. What you describe with the plants is common aphid damage so I wonder if your "fungus gnats" may not be aphids instead? If so, then eliminating the aphids should cure the problems for the most part.

What sort of potting soil did you use? What have you been feeding? Old potting soil, excess moisture levels and excess fertilizer use can only compound the problems be it fungus gnats or aphids.

Hope this helps.

Dave

Thanks for the response. I had just looked at some pictures of Cucumber Mosaic Virus, and they looked really similar. I was using Neem Extract to combat some aphids, that first appeared on my peppers. But I didn't think they were extreme, did not see many on Tomatoes. Unless they carried a disease. I used sterile potting soil the Perlite mixture with the other word I can't think of. But when I transplanted up to 4" pots I used a Miracle grow vegetable product. I also fertilized weekly with the miracle grow bottles that go into the sprayers. Except I put the solution into the self wicking grow kits and also mixed with water to bottom feed the 4" Peat Pots. Maybe I overfertilized. I attempted to not over water. I am thinking I should isolate the plants and start over.

If I understand you correctly then yes, WAY too much fertilizer. And that explains the aphids - they love all that excess N. 1-2 staged doses of very dilute 1/4 strength of normal is more than enough for most seedlings. And, if you used MG Gardening Soil rather than their potting mix then that too could be part of the problem as it is not made for containers (it's on the bag) and there have been several reports of problems with it in the past here when it is used in containers.

The Neem also needs to be used at a diluted strength on seedlings as does anything you use on them. They simply cannot tolerate the normal doesage mixes recommended for established plants.

If it were me I would hose off the seedlings well with the sink sprayer to remove the aphids, flush out the root balls to get rid of all the extra fertilizer, and repot them in a fresh, neutral potting mix. They may very well recover. Meanwhile, start some new plants if you have time.

Good luck.

Dave