Rusty brown spots on leaves

I think the TDS Pen is accurate since It says bottled water less than 50 PPM and my tap water at 190 PPM. I also check the PPM of the feed after each addition of the nutrients and watch the increases. I believe the last PPM of the feed was 1900. PH of feeds 6.25 to 6.4 Only several leaves had brown spots. Hopefully the flushes that lower the PPM to less than 1000 on all plants allows for normal / reduced feeding while insuring my cal & mag are being taken care of. The overall health of the plants looks good and they are ripening, can't wait to see the buds continue to grow in diameter and length . This is my first grow inside a small 4ft by 4ft tent. Not sure what the harvest will be like but I am hoping to get at least 2oz total from all 4 plants, do you think this is probable based on how they look at 8 weeks?

Excess.. It's not from too little of anything.. 3500 is obviously too high.. You've added too many salts and your plant can't possible use all that level of salts/nutrients whatever. Or your soil is very hot to begin with... Osmosis is how our plants absorb nutrients.. Not by direct eating.. Osmosis is very PH and salt sensitive. Why are auto pot feeding systems catching on with a lot of folks? Because plants absorb nutrients from the bottom up. Use less nutrients..

if ppm was 3500, more likely lockout. check labels. Calculate how much ppm of ca and mg do you provide? this will allow you to eliminate 1 of the 2 possibilities. If you provide plenty of Ca and Mg it is lockout. 3500 is crazy high... unless the accuracy of pen is off.