How often to water seedling in coco?

I pre-charged with Cal-mag/micro/bloom/ph'd water. And the seed sprouted out.

it's under 100w cfl light.

1. How often do i have to water?.

2. just plain PH'd water for 2 weeks?.

3. my Tap water shows 220ppm and 7.8 ph. can I use tap water to feed plant?

thanks.