leaves,yellowing browning on tip

leaves are spotitly yellowing and older leaves browning a bit on the tips. plant is about 3 weeks old and today i thought i seen a gnat in the pot and killed it. i checked the stem nearest the soil and noticed a white almost mold on it. does this sound like symtoms of fungis gnats. plant is still growing good just seems like it is working from the bottom up and once leaves are about 6 days old they start showing signs of yellowing. plant is growing good except that problem.
 
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