Help!: browning on tips of leaves on bottom leaves

Hey guys. I can't figure out for the life of me why my month old plants are browning at the tips at the bottom of the plant!!?! I think I am doing everything right, which is probably my problem, but does anybody have any idea what it could be??

Here is my setup and what has been going on:

-I am growing 6 plants in a well ventilated closet
-I am using an ebb and flow system
-They get watered once a day in the morning, the rock wool soaks it up pretty good and stay moist all day
-They have been vegging for about 3 weeks
-They are between 7 and 9 inches tall, about 7 to 10 inches wide
-I started using nutes 1 week into veg. I started with full strength for the first 2 weeks and I flushed the system this week with first 6pH water then 6pH water w/ 1/2 strength nutes.
-I have been watering them with that for the past 4 days.
-I have a 600W MH light about 2.5' above the plants. It seems a comfortable temperature under the lights, and the thermostat reads 78-82 degrees through the day
-Light cycle has been 18/6 since day one.
-2 fans in the closet blowing around plants all day, closet open to rest of room all day w/ large fan, overhead fan, and open window. I feel as if I have ventilation covered.

There is also this green mold that is growing on the rockwool. What exactly is that? and is it harmful to the plants?

I realize that I may have duped up with the nutes at the beginning. What affect could that have on them now?

Those pics are a few days old and the browning and mold have both been getting worse.

Hmmmm what could it be?

Over fert? or ph

yea u definetly started with the nutes to early!!when u first start the plant can survive on the soil alone for about a month.You should never add the full strength of nutes the first time r applyin them to ur plant.It could shock em' burn em' or even worse kill em!!!It also sounds like ur plants have a nute overdose!!im not sure what nutes ur using but im pretty sure no matter what it is ur not supposed to put them in with every watering but for me to be positive on that id have to kno what kind of nutes u have????

I have Ionic Grow. I was told from the grow shop guy that this is what I need for the vegetative stage. For flowering I will get something else.

So if I have nute burn, I should be flushing out the system right? I've read that you should flush w/ 1/4 solution, so I'm going to do that for like a week. Then I'm going to up the dosage gradually.

I check pH regularly and keep it @ 6.0.


Does anybody have any thoughts on the green mold growing on the rock wool? I hope its not deadly!!

Thanks for the tips!