Answer: Based on your description it sounds like your seedlings are "damping off" due to over-watering, so I would suggest that you stop misting them. Water only enough to keep the soil slightly moist like a wrung out sponge. Also make sure they are in very bright light and have good air circulation. Finally, make sure they are thinned adequately to allow light and air to circulate freely between them. Here are some pointers on seedlings you might find useful.
As soon as they start to sprout, put them immediately into bright light. Make sure there is also some air circulation where you keep them as stagnant air can encourage fungal growth. Next, make sure the plants are thinned enough to allow for ample light and air to filter through them. Also, do not over fertilize them. They do not need fertilizer until they have several sets of true leaves. Try watering by dribbling water gently and slowly out of a small pitcher onto the soil rather than spraying them -- wet foliage will also encourage fungal growth. Finally, make sure all of your tools and equipment are clean and that you are using a relatively sterile potting mix such as a soilless seed starter of peat, vermiculite and possibly perlite. Other causes of damping off can also be too high or low a temperature or too little light -- many gardeners find it necessary to use supplemental lights for seedlings. Last of all, you might have luck watering them with chamomile tea when you first see the problem begin to appear.
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