overnight wilting/death, nitrogen deficiency or root rot?

Alright guys,

Having an issue with my plants. Saturday they looked great about 5 weeks into flower. Sunday i noticed Yellowing lower leaves so i did a reservoir change. Monday the yellowing had overtaken the plants. Tuesday morning, one completely wilted. I need some help diagnosing what I'm doing wrong outside of the diagnosis charts.

Grow Media: Hydro RDWC 5 gallon buckets
Nutrients: Advanced Nutrients Sensi Bloom
Water readings: pretty stable 5.5-5.8 ph and between 1200-1450ppm
Temperature: 61 at night 77 during the day.
Reservoir temps: 62-68 degrees
Equipment:
1000W HPS
4x4 tent
45lpm air pump 2 air stones per bucket.
20 gallon reservoir outside the tent




Other notes: Maybe too long between reservoir changes? i had just been topping off nutes.

Not enough air in the buckets?

Maybe I switched over to flower nutes too soon? causing the start of nitrogen deficiency? (Switched the same day I switched to 12/12)

could it be root rot? They don't look brown or slimy but i did notice a little bit of an odor although I have no idea what root rot smells like.

added pictures of both pictures and one i took 5 days ago.

let me know what you think. Your help is appreciated.

take pics in white light so proper color of plants can be seen. some closeups would nice. are you using both A and B of the fert? you ppm seems a bit high. Is it possible that you're over doing the phosphorus? are the plants getting some nitrogen?

Hard to tell if it's root rot with those pics