cana coco and tiger bloom
As for the runoff 7 is even too high for soil, for coco it's worse. You want to be under 6 pH runoff in coco, maybe 6.2 in the last half of flower but I've seen coco grows where it was 5.5-5.7 all the way through with great results. I'm not positive as I use soil, but I believe in coco you need to periodically flush because coco tends to hold salts in if that is the right term. So salts and high pH seems to be your issue.
As for nutes tiger bloom is all you have used for bloom nutes? Tiger is really a secondary bloom nute in the fox farm system. It works best with big bloom which is quite weak but works very well and contributes to the overall health of your plants. Big bloom is great for seedlings and should be used throughout the grow and in conjunction with smaller doses of tiger once buds begin to form, tiger is very strong and only the most nute tolerant strains can handle even the recommended doses. I only use tiger through weeks 2-6 of flower every other fed at 1/2-3/4 doses.
In the future definitely grab big bloom in large amounts, and the three solubles if you can(open sesame-beastie bloomz-cha ching) using these along with tiger at 1/2 strength doses make for a great system.
But being you are in coco I can't give details or experiences because I use soil.
Do you use a cal-mag product? In coco it's a must.