Leaf Edges turning Brown, Yellow Spots Starting to Form on Leaves

I have 4 plants(2 autoflowering Road Runners and 2 BubbleGum Skunks) All four are starting to have brown edges on the leafs and some yellow discoloring. They are all about 7 weeks old. I use a flora Micro and Flora Bloom nutrients,growing in coco, with a ph level between 6 and 6.5 and a ppm level around 400. What should I do to fix this problem? What could the cause be? Should I flush out coco? The RR's are starting to flower?

Looks like PH but if you are sure it's not then it may be Magnesium issues may need epsom salts if it is. Anyone else thinking an issue with the uptake of magnesium? not necessarily the presence but the uptake.

not 100 percent sure on ph, should i make sure ph level is correct and keep feeding with current nutrients or should i flush the plant out and go from there. How can i tell if the plants are having a magnesium issues? My 2 bubble gum were the first ones to show these symptoms and just in the last 2 days the road runners drastically changed(browning on leaf edges)All 4 plants are in the same enclosure under the same light

i have 5 plants that i just put on flower i got to get pic's up but they look pretty close to this!! starting from the top all the leaf's are turning yellow and some browning

i figured out what happened with my plants and wanted to share this information with you. I am using coco as my soil and the ph level built up in the coco and locked the nutrients out, I had to flush the coco with ph'd water and then start feeding with nutrients right away. The scarring(discoloration) will always stay, its the new growth you want to watch.

As hippy smoke says, looks like magnesium deficiently,A quater of a t-spoon of epsom per liter should do it. hope this helps.