Phosphorous Defiency???

I'm growin indoor... over the last few days ive noticed grey spots coming on some lower leaves and also some rusty spots. the leaves affected are curling up, going yellow and, obviously, dying ... i dont want it to get any worse im loosing too many leaves... i have some pictures of the problems below.. im thinking it is phosphorous defiency by the look of it but i could be wrong. im using miracle gro all purpose nutes (blue stuff) 24-8-16. i water it just over every week. this time i used my nutes, time before that i used no nutes (which was when i saw the problem arise). have it under 200w cfl and have a little fan on it too...
i'd appreciate any help on this im a bit worried...

any questions just ask....



grey spots
a dead leaf i pulled off
grey spots
rusty spot

plants growth is slowing down i noticed too

the leaf you pulled off wasn't dead yet. leave those on until they're colourless and saggy/wilted (i.e. dead)

your problem is miracle grow. not a suitable nutrient for cannabis. causes nothing but problems, like what you're experiencing

this is likely a combination of PH and nutrient imbalance, also a lack of trace elements

there are nutrients at your local hydroponics store that are more tailored toward cannabis

best you can do imho is feed with pure water until you notice healthy even growth, then start feeding again with something else

oh ok ill stop using it so.. should i flush the plant as i just used miracle grow yesterday when watering it?
i appreciate the reply man thanks