Could really use some advice here..

OK so the first problem is the main concern as its affecting multiple plants across 2 different strains. The problem tends to start near the lower part of the plant and progresses upward. It starts with brownish/grey lesions and typically works its way out from where the leaf meets the stem and progresses over the entire leaf causing it to curl up and die. It kills the big fan leaves first before moving on to the smaller leaves. This plant is 2-1/2 weeks into flowering, and probably 2 months in total age. Runoff pH is approx 6.5-7.0. I use the dropper kits so I don't have an exact number. Medium is a potting soil called Edna's Best in 2 gallon containers mixed about 60/40 with perlite and I use FF trio for nutes, never using more than a tsp/gal of GrowBig or TigerBloom in any combination. I use RO water and substitute 1 tsp/gal CalMag every other watering (watering works out to roughly 3 times every 2 weeks). Temps are 78-80 lights on and 75ish lights out. I know I could probably just flush and start over, but I'm all about learning and I want to know what's causing this problem for future reference. It almost looks like the leaves are rotting, but it seems to spread the same way on each plant, so I'm assuming that's not it. Here's some pics all from the same plant (last pic is underside of a leaf):




My other problem I originally thought was a calcium problem but it continues to spread regardless of my use of cal-mag. This problem is only occuring on one plant but its spreading rapidly. I flushed the plant a few days after an initial treatment of cal-mag had no affect and the problem continued to spread. After flushing I gave it a very light (1/4tsp) feeding of FF GrowBig (It looked to have a N deficiency as well) and some cal-mag. It looks so much like nute burn at this point but it was doing fine on higher doses of ferts throughout its life and I have yet to feed it again since that initial feeding with the flush. Conditions are all the same as above.This one was budding up real good too, but has since slowed. Here's a few pics of the damage:


And if you could let me know in your response's if you've actually encountered these issue's or if you're going off second-hand knowledge. I'm not judging, and all information is welcome, but hearing from someone that's been through it is sure to be invaluable. While I hate running into problems, I find learning from them enjoyable. So somebody, please help me learn what I'm doing wrong here!

Whoa, there's a lot going on there. I'm gonna try to help but I'm still new and learning like you. I don't have a clue what could be wrong with your plants in the first pictures, maybe someone will more experience can tell ya that. But I had a plant that looked similar to your last in the last set of pictures. What I had going on was a salt/chlorine toxicity from using tap, don't know if it could be the same since your using RO, but maybe an expert will see it now! Good luck, I hope you figure it out!

It appears to be a case of Phosphorus deficiency. That should be an easy problem to fix. It is the same problem on all the plants with a little nitrogen deficiency to boot. The best recommendation I have is: Fertilize more. Best of luck, Prof.Snook

Thanks for the suggestions guys! I gave them a decent dose of ferts and I'll keep an eye on them. If they don't improve, its been 3 days and they have not, then I'll have to approach it as a lock out causing the deficiencies. I suppose the salt build up could be causing a toxicity. Either way I see a flush in my near future...I hate flushing mid-flower but slowing them is better than losing them I suppose!