First time grower needs some advice please

[wheely]

So, i germinated the seeds,
then put them into rock wool squares and under a 250w light (blue spectrum) at 16/8 with ionic nutes in the hydro systems (ebb)

they been under this for 9 days now are about 4-5cm high

air temp - 26-28 degrees c
humidity - 25 %

Q.- Am i reading the humidity correctly ? - i have the digital gauge on the surface where plants are with a cardboard piece covering it from light, but some air movement over it

Q.- should the plants be under this 250w for 6-8 weeks veging or the 400w full spectrum light?

Q.- Should i change the water and nutes every 7 days?

Thanks for any help.

 

[jlt1202]

you should have the light on fro 24 hrs, 18/6 at the min. 250w should be ok for veg but only for like 2 plants, anymore you need more light for space your working with.