R.I.P.Seedlings

I lost three of my men in the line of duty today, two are in critical condition, and two have minor bruises and scrapes. The culprit is damping off. The seedlings are 3 weeks old, under fluorescent light, in backyard potting soil(i know a mistake), at about 17 celsius. I don't know if it is from over watering because I have only been watering once everyday about a tablespoon. The problem is more likely fungus gnats. But the question is, is there any way to save my soldiers in critical condition (browning and thinning at bottom of stem), or are they done and done

Sorry to hear that man, a few of my soilders got tooken out too... Best of luck to you.