plants dying with gold spots on leaves

1. i'm using ebb and flow hydro
2. watering once a day
3. growing in rockwool
4. i'm in the 5th week of flowering
5. plants looked great 1 week ago
6. 4 plants in a 3' x 4' space
7. 400 watt MH

i got back from a trip and found two of my plants with gold spots, leaves curling, and plants appearing to die. i took ph and it was 5 or possibly lower. i drained all of the water and then poured new water over the rockwool after using ph down to get it to the right ph (i use 5.5 to 6.0). this water remains in the system for the watering.

came home today from work and my two other plants in the space appear to have started the same problem. these two other plants are the strongest in my bunch and now they are taking a hit and looks like they might die quickly.

is this nutrient deficiency from lockout form low ph? i looked at other photos on the site and didn't see any that showed the large amounts of "gold" color that are on my leaves.

any help would be much appreciated. this is my first grow and it was going so well, but now seems headed for hell real fast.

thanks in advance

can anyone provide some advice/help? my plants are getting worse...