1st Grow Hydro, Leaves Yellow & Brown Spots, Help!

Hi, I'm Kitty and this is my first grow. Here are the details:
What type of medium; soil or hydro? HYDRO
Indoors or outdoors? INDOORS, CABINET GROW USING COOL CAB
What strain? UNKNOWN BAG SEED, DUTCH PASSION FEM BLUEBERRY, FLO & STRAWBERRY COUGH
How old are the plants? UNKNOWN IS ABOUT A MONTH OLD AND OTHERS ARE 2 WEEKS OLD
What type of lights and how many watts? 400 WATT MH BULB
How far from the lights? 18"
What is your watering frequency and source of water? EVERY 2-3 DAYS, DISTILLED WATER
What, how much and when was it fed? NPK? MOONDUST, SWITCHING TO FOX FARMS NUTES TOMORROW WHEN I GO TO HYDRO STORE; HOLDING BACK ON THE NUTES SOMEWHAT B/C NOT SURE WHY THE PLANTS AREN'T HEALTHIER. WHAT IS NPK, PLEASE? WATERING IS CONSTANT DRIP, FOGGER AND RESERVOIR WITH ROOTS HANGING DOWN INTO WATER (ROOTS ARE GETTING BIG, VERY HEALTHY LOOKING).
What is the medium/runoff pH and PPM if in hydro? ASSUMING RUNOFF IS WHAT IS IN THE RESERVOIR, PH IS ALMOST ALWAYS STABLE AROUND 6, AND PPM IS 150, AGAIN, AFRAID TO FEED TOO MUCH SINCE I DON'T KNOW WHAT THE PROBLEM IS.
What are the temps and humidity in the room? COOL CAB RUNS A LITTLE WARM (IRONIC, HUH?), UPPER 70'S TO 80 DEGREES F, I MAY NEED TO REPLACE THE EXHAUST FAN TO MOVE MORE WARM AIR OUT OR IS TEMP OKAY? HUMIDITY RUNS BETWEEN 34-40%.
What size pots? 3" NET POTS
Any bugs? Look real close. NO BUGS
Any other pertinent info? THIS IS MY FIRST GROW, AND FIRST TIME EVER USING HYDRO TO GROW ANYTHING. I'VE READ A LOT AND WATCHED VIDEOS ON BOTH SOIL AND HYDRO GROWS, BUT ADMITTEDLY HAVE NO IDEA WTF I'M DOING, JUST HAD A BUNCH OF MONEY TO THROW AT THIS PROJECT AND TRYING TO MAKE IT WORK. SAD MY BABIES LOOK SICK, I WANT THEM TO HAVE WHAT THEY NEED! THE TOPS OF THE PLANTS (NEW GROWTH) LOOKS GREAT, BUT BOTTOM LEAVES ARE DYING, YELLOWING AND GETTING BROWN SPOTS ON THEM. SHOULD I TRIM THAT DEAD-LOOKING GROWTH OFF? WHAT COULD BE THE CAUSE OF THIS?

ALSO, DP FEM FLO LOOKS TO JUST BE STALLING OUT ON GROWTH (3 SEEDS OF EACH PLANTED, 1 FLO BEGAN TO GROW, ALL 3 BLUEBERRY GROWING, 2 OF 3 STRAWBERRY COUGH GROWING, AND 1 UNKNOWN IS IN THERE), BUT DP FEM BLUEBERRY IS DOING REALLY WELL (CONSIDERING IT'S DYING WHILE GROWING, APPARENTLY), AND ONE OF TWO OF THE DP FEM STRAWBERRY COUGH LOOKS GOOD, UNKNOWN IS GROWING LIKE CRAZY, ALL OF THEM ARE ACTING THE SAME WAY, THOUGH: BOTTOM TO MIDDLE LEAVES ARE YELLOWING, GETTING BROWN SPOTS AND DYING WHILE THE TOP/NEW GROWTH LOOKS HEALTHY.

THANKS FOR ANY HELP!

KITTY