What is going on with my plant

Hello, my ladies are in the 4th week of flower, everything is coming along nicely and they are looking really healthy. Just a few of the leaves of one of them (la kush cake) are starting to show signs of something not being right. It's just a few leaves here and there with the majority looking really good, but what could this be?
Feeding foxfarm big Bloom and tiger Bloom both once a week currently (2 tsps per gallon) and PHing water to 6.3.

Thanks

Magnesium deficiency probably

Add some cal mag next time.