Brown spots on my fan leaves

I hope someone can help.I have 4 very awsome looking plants (an indica sativa mix 60-40) growing in an ebb and flow system.My medium is coco croutons and pea gravel,and my nutes are floranova bloom at about 700-725.Thats the best guess just going by the labels measurments. I dont have a ppm meter yet but i am working on the wife.My light is a 400 watt hps at about 3 inches off the top of the tallest plant.
I am three weeks into bud And ive noticed some brown spots just on the fan leaf edges.They started about 5 days ago(about the time i changed feeding schedule.I was pumping nutes 4 times a day 2 in the light 2 in the dark,thought it was too much at dark time so i cut one dark feeding. about 2 days later i noticed a few spots on a couple of leaves,so i switched my feeding schedule back the way it was. now abot 1/8 of my fan leaves have them.I have read some threads and some say it could be a potassium def. I also read that coco is known to leach potassium.could my coco be leaching that much this late.They veged for 1 month before i started budding and had no ploblems till now.Here are some pics

Well i just did a little more reading and found i might be over ferting them.I am using floranova at 1 1/2 teaspoon a gallon(about 725 ppm)I have been uping the nutes slowly since bud day one from 1/2 teaspoon to 1 1/2 in three weeks.thought they could take 1/2 teaspoon climb every week.turns out i may have been wrong. This sounds a little more like my problem than a potassium def.does anybody have any opinion,idea,advise,anything?

nitrogen overdose my man its the first sign if not its got to be a nute problem drain 3 quaters of ur res an top up with fresh no nute water and see how u go

what to do if it is a nitrogen overdose because I have the same problem

its not nitrogen overdose bigwity as a matter of fact i cut the available nitrogen in almost half from grow to bloom.the nitrogen in my grow is 7%and only 4% in my bloom,but i do agree its a nute problem i believe from salt buildup

id like to see pics JLpr