There is everything wrong with it, this is very bad advice! the cotyledons die off that is normal, the first true serated leaves die off that too is normal. Any other leaves dying off is not normal and is an indicator that you have a problem!
pic 1 looks like a Cal def
pic 2 looks like an N def
pic 2 looks it is sharing a pot with another plant???
those soil/nute testers are crap and pretty much no use to an MJ grower, you need to learn to read the plant, it will tell you what it needs/wants.
How are you ph'ing your water?
what nutes and how often?
What kind of soil is that ?
How old are the plants?