Dying lower leaves

[Night Prowler]

I have plants in 2 stages, 4 weeks apart. Recently started a new strain "early misty" from seedlings. The older plants were getting too much Nitrogen as evident by the forest green color of leaves, so I over watered them to flush the roots and have added no food in 2 weeks. For the past week ive noticed all older plants bottom node leaves are turning yellow (just the bottom 2 so far) and now have dyed and turned brown on the ends. Ph 6.0, light 40watt per Sq ft. Temp 80* + Co2, No bugs, soil mix is 1 ver, 1 per, 1top soil and 1 cow-compost. I also use distilled-purified water.
The new sprouts are doing something different but I may be over watering. They are looking a paler green color, some yellowing and showing brown spots. Im a vet grower so will understand a simple answer.

 

[Torco]

Yellowing of lower leaves is a natural thing for MJ plants to do.
you flushed the plants 2 weeks ago and you have not givin any nutes for 2 weeks. thats to long to go with out nutes, were there any sighens of nute burn on the tips of the leaves?? Distilled water is not very good for MJ plants. you would be better off just using tap water, thats just my opinion.