Mold (OR algea) growing on top of potting medium can be caused by all of the things you mentioned, plus a few more reasons. Generally, however, it occurs when the mix is too slow-draining (fine texture causes this, as opposed to a coarse texture), is watered too requently, and/or there is not enough air circulation in the vicinity.

What color is the 'mold'? That'll help us decide just what it is.

Oftentimes, the conditions that allow for the growth of mold, mildew, or algea (which are not problems for your seedlings on their own) can also invite a real pathogen outbreak such as damping off. That's a fungal vascular disease that can wipe out a crop of seedlings. In other words, the kinds of stuff that begins to grow on the top of the potting mix is a warning that the conditions are present for real problems to occur.

Be sure to add plenty of perlite to your potting mix to assist in the porosity by improving the texture. Also, though seeds appreciate warmth during the germination process, they do much better in cooler temperatures once they've begun to grow. A small fan can add the required air circulation, if needed.

Add chlorine bleach to your water. Maybe 1/4 tsp per gallon. It will help to clear up the problem. I am more concerned about starting tomatoes and squash so early. Do you have a greenhouse? Squash will begin blooming within 60-70 days, well before we are frost free. The seedlings may become very spindly before spring gets here.

Thanks for the advice. The mold seems to be white and cotton like. I'm going to enlarge the drainage holes, and turn the thermostat down a couple of degrees, and see if that helps. If that doesn't help, I'll try the bleach method. The Spaghetti Squash was a surprise from the supermarket. The seeds inside the squash I was cooking for dinner one night about 2 weeks ago were already starting to sprout so I just stuck them in soil, and their taking off. The tomatoes are the early kind (Fourth of July Hybrid). I just started about 6 seeds, and I saved some seeds to start later. So far my tomatoes haven't sprouted, and I put them in the soil about 1 week ago. My kitchen serves as a make shift green house. I have 2 large south facing windows with large ledges.

I started my tomato seeds using tp rolls just a few weeks ago. I have had a white mold growing on the sides of some of the rolls and started treating them with chamomile tea (sprayed the seedlings AND the outside of the roll) and so far it appears to helping. Are you still having a problem?