Ph run off water at 5.0- signs of deficiency

Hi everyone.
this is my first grow, growing in soil and my plant is on second week of flowering. During the last weeks of vegetation my plant started showing signs of deficiency: brown spots on leaves and leaves dying becoming rusty.

Just got a digital ph meter. I fed the plant with organic nutrients(biobizz: topmax, biogrow and biobloom). Using ph up I fed the solution and it indicated a ph of 7.3. Measured the ph of runoff water and it was 5.0!!!!! I mixed some of my soil with distilled water, let it stand and the ph was 6.1. I don't know which of the indications is more correct. But seems like the soil would be around 6.1 or does the runoff water indicates the actual ph of my soil which means that it might be at around 5,which is very acidic. Any help or ideas? Some fotos might give you an idea of the rusty leaves I get

IMO- buy a soil pH meter, there dirt cheap.
If your pH is off you'll start to lock out nutrients.

could be nute burn. rusty spots on lower leaves is usually an indicater. watch your nutrient amounts. id suggest a ppm meter(blue lab is what i use). for soil check the ppm of the water you feed with and maybe even the runoff. hope that gives you some insite.

Thanks guys. Just found a cheap ec meter from eBay. Ism going to give it a try! Thanks