Hey BTT just chiming in mate.
I've read through your journal and there's a few things I've noticed.
I don't know the dimensions of that closet but it only looks like 3-4sqft.
A 600w is gonna pump out 90000 lumens.
That equates to about 20K+ lumens per sqft.
Too much...10000 per sqft is perfect.
I would of had that 600w at 4' above seedlings, no closer.
You should really be operating with a 400 or 250 in that space.
You have a lot of vert' so make the most of it when running all those lumens.
With that many lumens you don't need reflection either.
Good move getting rid of the mylar, you don't need it.
Also never have a fan pointing down onto the plants, your just blasting heat from the lamp onto them.
Having your fan on the floor was a good suggestion.
Other than that, your main problem is overwatering.
Like borntokill says you need to learn to judge the weight of your pots.
When they're light to lift, thats when you water.
I mean really light like they are when they're dry.
Now that your under cfls they will use less water so be carefull.
Your seedlings may only need watering every 10 days or so to begin with.
When I put my seedlings into the pots from germing, I water them in and then don't water for 2 weeks sometimes.
Let them grow strong roots as they search for water.
As borntokill says your trying to hard and killing them with kindness.
MJ is a weed and will grow quite well with little care and attention.
Plants take ages to come back from moisture stress, weeks in fact.
Keep at it bro, you'll get there.
No more water for a while OK?
I really want to see them back under that HPS at some stage soon