i'm a newb so take this with a grain of salt. your plants look awesome. get a soil moisture meter. i water every 5 days in flower in 5 gallon pots maybe 3/4 gallon with nutes, skip nutes every third watering. i can't imagine a plant going 18 days no water. maybe you run high humidity or temp, tell us your temps and humidity. let us know your lux measurement.
I went to the hydro store in victorville, walked around every light in their hydro room setup with a nice digital light meter.
a 6 light t5 puts out same lux at 8" as a 1000 watt hps does at 3 feet.
I bought the t5 setup, same lumens i got a chart to prove it.
ps I like fox farm no regrets read the label bro
peace