They already *were* on straight water for 2 weeks, they are 3 weeks old. I realize they look like they are 6 day old seedlings, but they are 21 days old.

I assumed since some people water with tap water (which would be their definition of pure water) which has a ppm of 200 on average, that 175ppm is basically the same thing as untouched tap, with the exception of it having beneficial nutrients instead of useless crap in the tap water.

PLUS, the cotyledons started showing signs of yellowing

again these are 21 days old