Grow Mediums reoccurring plant killing problem

[-K-]

Hello! This is now a second time in a row I'm losing a plant to same problem, at the same stage of growth.
The plant started becoming necrotic and crispy when it reached age of 10 days, and is been getting worse fast in few days. Growth was explosive before this sudden fall. Im using AN pH perfect series 1ml per litre. My grow room (bathroom) temps are not high, im still using only 90w of led. I forgot in hurry to take a photo of roots in hurry, but the look nice and white to me. I can upload a photo of them later.
What could this be that kills my plant? Low humidity? Low root oxygen?

 

[jingo]

Are you checking pH? That pH perfect has failed one grower here. He found he needed to pH down his water before using the nutes. Then it all started stable.

Anyway, looks like pH swing. You will need a pH meter and a ppm/TDS/EC meter top get a clear picture of plant needs.

 

[IndicaIVoz]

The crispy you are referring to straight off i would say is chlorine are you evaporating your water if it is tap.can you also list the full grow details.
Another thing il add is if your using AN Sensi or conni 1mpl is way to high this would be helping to fry them also.