What is this?

Wondering what may have caused this? Plant was growing fine throughout veg( 6 weeks),moved to flower 10 days ago and notice some of my leaves with this. Look everywhere for pictures of plant problems and have seen nothing like this. Growing in soil, pro mix ultimate organic, water every 4 to 5 days. growing in 18 gallon tub so holds water pretty well. Using cheap miracle grow bloom booster nutes, but only fed once since in flower. Any ideas?

Nute burn from guess what ...cheap miracle grow bloom booster nutes, flush https://www.rollitup.org/blogs/blog32237-flush-baby-flush.html

It does look like nutrient burn from too much N, but I do wonder how much water is that tub holding? These plants do not like (wet feet) and if that is the case your plants are going to look crappy and exactly like nutrient burn . From my past experience that is.

I know its not over watering. I really haven't fed them much, strain must be really sensitive to nutes. My first grow went awesome with miracle grow. I guess I won't feed until she shows she needs it. My first grow made classic mistakes of planting 3 in same tub, used miracle grow soil, and nutes, and went swimmingly. Got 4 ounces off 3 plants. I will just back off and watch. Any other suggestions are welcome. Still new, but reading constantly to get this right. Thanks for the replies. N8