pythium starts early..but conditions make it prevail..
good practice is using damp off when taking clones..
some water treatment methods like heating, UV, ozonation or even chlorination can help keep it at bay...
Pythium Aphanidermatum and Pythium Irregulare can cause the most damage in ebb and flow systems. This is because the organisms form a swimming spore stage that can move in water and attack your plants very quickly.
it moves in the water..this is why daily top row watering in not a good thing for you.
i recommend watering every third day, and covering the holes to keep it from drying out as fast up there.
also you already know that its worse at a higher ec..and the ppm in the media vary according to the drying cycles.
finally your coli is dtw..are all the stages before the same?...and what is your cloning media..jiffy?
hope this helps..http://www.crophouse.co.nz/files/CG_...thium-view.pdf