Rockwool 1st Time - Help!?

Hey all, this is my 1st time with rockwool and I'm a little confused why the plants are growing slowly and a couple look terrible. I'm just coming off a very successful DWC Bubbler Grow (see my signature) and have got a new Ebb & Flood setup with 5 different strains. Here are some facts about the setup along with some pics. I'd appreciate any advice you can share about experiences with rockwool as it's the only thing really different about my setup vs. the DWC grow.

Plants are about 2 weeks old
3X3X7 Home Box Grow Room
Ebb & Flood - 25 Gallon Res
6x6x6 Rockwool (Ph 5.8 soaked for 3 days prior to planting)
Flood 4 times per day for 5 mins each (3 day/1 night)
430 Watt Hortilux HPS on 18/6 Lighting Schedule
Daytime Temp: 76 - 79 F / Night Temp: 66 - 69 F
In Line Fan - 460 CFM
Ph: 5.8 - 5.9
PPMs - 300
R/O Water
Botanicare Nutrients with 1/2 strength recommended for seedlings (Pro Grow/CalMag/Liquid Karma/Hydroguard)

I started the plants with R/O water and a very low addition of Liquid Karma (much less than recommended). Over the last 10 days, I have very gently added the rest of the nutes and am only at about half strength of what Botanicare recommends for seedlings. This is the same that I used for my DWC and the plants were 10x bigger at this age and were generally healthy.

Help!?

way too much water and diffrent plants react diffrently to nutes. dont mix plants only flood once a day or less if the cubes are soaked rock wool holds alot of water

Yea, overwatering sounds like it. Rockwool will REALLY hold the water in, so you shouldn't have to flood that often.

For sure, especially those 6 inch cubes, they hold a lot of water. I use them outside in the sun, and water them once a day.

HTH