Nice looking light buddy, fits the tent perfectly! Your plants are looking quite happy and will be even more happy with the new light heading into flower. Also, that spotting on the "dodgy" leaf doesnt look like its spread any where else. Could of had nutes spilled on or brushed up against something and got damaged. With stuff like that, as long as its not spreading to the rest of the plant I wouldnt worry about it too much.
I dont know much about bottled nutes so I cant help ya there
Cheers dude and keep up the good work