What's wrong with my baby?!?

Noob here... my first grow is a lovely little girl who's just coming out of veg and into flower.
In a pot of high quality soil mix,
Lives outdoors getting full sun,
Watered with half strength SeaFeed 3 in 1 organic fertilizer every three days or so when the soil gets dry.
When I left her for the weekend she was fine, about a foot tall, healthy green with nice big leaves, and when I came back the bottom two leaves had turned completely yellow and pretty much fell off in my hand.
Also, on the underside of the dead leaves there was a bunch of crap that looked like orange sugar crystals, but just crumbled off like powder when touched.
The upper leaves are still looking pretty good, but a couple of them have a bit of brown starting right at the tips.
I'm freaking out a little - the color seems to indicate a sulfur deficiency, but I don't know what's causing the brown spots, and I'm wondering if the orange stuff is fungus?
Any suggestions would be greatly appreciated!

doesn't look like much of a problem
maybe it was overfertilized a lil bit

orange sugar crystals? Sounds like that shit they spray on grass either pest killer or weed killer

Thanks guys,
I've given it a good watering with just plain aged H20 to flush it - The upper leaves are still looking fine with just a tiny bit of what looks like burn mark on the very tips of two leaves.
I'll keep an eye on it and see how she goes - it doesn't look like there's any of the orange stuff on the other leaves.