i would have the water level with the bottom of the net pots, just touching the underside of the plastic netpot at this stage.
the pic is hard to tell, but looks like this is where its at .
I wouldn't top feed them either, you want the roots to spread out and look for water, and the airstones should be providing enough D.O for them to start getting their feet wet.
I would also increase the feed to 0.4EC to be honest, they look to be a couple of weeks old, and you are running R.O water.
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