I do think that a fan might be unduly drying the upper part of the containers. I don't see a need for fans until there is a seedling growing. Good viable seed and proper warmth are very important. I would think that one element has not been consistantly there if part of the seed comes up and much does not germinate......moisture, warmth, viable seed, and sufficient time.

Are your seeds fresh? Onions seeds have a low germination rate after 1 year.

Your lettuce died: It may be damping off.

When they are under tight cover I don't have to water them. It stays moist.
After that I water them once every 3-4 days.

I have learn to give them a break and let them growth at their pace. I limit my trip to the basement once a day.!

And I have learn to be patient. The germination time written on the package is the optimal rate with the optimal temperature, soil, light.... Mine take usually longer.

I've had good luck germinating the seeds you described first, then put them in soil. I take a plate, put some napkins on it, put the seeds on that, put more napkins over the seeds and then keep this wet and in a warm place. Some of the seeds you describe (lettuce) require some amount of light to germinate.

Here is a link that might be useful: Enter The Free Seed Drawing

Turn off the fan and lay some plastic wrap over the seeded surfaces. You don't need to tuck it under, just try laying it on top.

As soon as you get sprouts, remove any plastic covering.

You aren't using any real compost in your seed starting medium, are you? Just use a sterile medium for starting, then you can transplant them to larger containers with compost included if you need to.

Sue

You might also want to review all the step-by-step- FAQ's posted over on the Growing from Seed forum. ;) Lots of help available from them.

Dave

Here is a link that might be useful: Growing from Seed forum