I hate to tell you this,really i do but if your fertilizing seedlings you really need to read the grow faq & not skip one single folder in it.
Seedlings require nothing except light & very small amounts of ph'ed water,you dont even think about using fertilizer until your a month or better into the grow.
Unless you have expensive seed bank seeds you'd be better off starting over with fresh dirt & seeds,in all likelyhood you have damaged the seedlings to the point where their growth rate will not be normal.
Seedlings can & will die off extremely easy from over watering which is what flushing is,to flush you take at the very least the same volume of water as the pot size & run it through the plant,a one gallon pot would need one gallon of water & so forth.