Water the soil and not the leaves. Your soil looks fairly dry. Could be many things to be honest.
Check your pH and then maybe give the plant a little Epsom salt along with extra nutrients.
What's you temperature and humidity at?
I bet that's all it is. At that mixing rate, it's pretty safe to use as a foliar feed. If the lights were on, it may have sped up the evaporation making it more concentrated causing minor spots. Keep a mister of plain water nearby to mist leaves that get splashed when feeding.
My other thought is the possibility of the ec of the soil immediately around the plant became a little higher than it liked as it dried on the top layer of soil after its feeding. You can mist the top layer with plain water to keep it moist in the days after feeding when they plants are young. Mulching will help protect your top layer of soil from drying too.
Epsom Salts are very helpful as Troutman said.
Either way, nothing to worry about. They're outgrowing these issues!!
It would be in your best interest to get a EC or TDS meter and measure the amount of fertilizer you use. The EC range is 1.3-1.6 and the ppm is 650-800 for a light feed using those fertilizers. Also if you are using RO water you need to supplement with Cal-mag. before using Maxigro and maxi bloom.
You should Water the soil and not the leaves. Look at your soil looks fairly dry. Check your pH and then maybe give the plant a little Epsom salt along with extra nutrients. What's your temperature and humidity at?