New problem starting with my leaves?

[Donz]

hi all. im in week7 of flowering. plants been super healthy all the time. im growing in soil 3 gallon pots in a 4x3x2 closet. i feed every other watering with no problems at all. this time i watered with usual tap water that i always use and started to see some problems, rust/brown spots on my leaves and discoloring. only 1 thing i changed, i bought my nutrients from somewhere else, rather than my usual shop. i always use the powder cheap nutrients and they've always worked for me(this is my 5th grow). could it be a simple deficiency? lockout? any advice?

 

[Donz]

went to my usual shop today and bought my usual nutrients. guy told me that mixing calcium with other nutes will usually cause a lockout, or at least this powder kind of calcium(and i indeed mixed 1ml cal with some mag and PK in my last feeding). i also got a new ph meter and it seems that i have some fluctuation going on. ph went from 7 to 5 when i test added nutrients to my tap water. hope this would be the end of my problem, gonna wait a few days for my next watering, go back to using my usual nutrients and see what happens. will update soon.