Wow big surprise another plant problem

Ok the edges of some of the bottom leaves are yellow and have redish spots looks like Mg deficeincy. Then today I noticed(compared to my other plants)that some of the leaves are a bit light green like a N def. But the tips on some of the top leaves are burnt looking. So Im confused on this. I flushed the system about 4 days ago and it seemed to help. Lastnight I topped of the res and had the PPM at 860 and 6.9 liters of water. Today when I checked it had 6.2L and the PPm climbed to 890. So I know that obviously the plant is taking more water cause there were to many nutes in there. So I lowered it down by adding water back to its normal 830. The only reason I added a bit more nutes last night was because of the discoloration. So any ways to sum it all up the plants are about 2 months old and are preflowering. Under 600 watt MH 20/4. Using Botanicare Pro Grow and Earth Juice Microblast. Have PPM at 830.
Oh and I have the PH at around 5.7. Was thinking of letting it go up to about 6.0 for a night to see if it would help with the Mg uptake. But I dont know. I looked on here and around on the web for info on all these symptoms in a plant but cant really find what Im looking for. Most threads in here and info online is for just one of these symptoms. So I'd be thankful for any help.

How about you water it with plain ph'd water and dont come back for 4 days.

I think you'll see whats the problem.

that first pic is lookin like P deficiency-yellowing leaf edges, tips bending down and curling up. the second pick looks like Iron def. these the same ones?
and Im gonna have to agree with Boneman that your ppms are probably too high. I have had P and Mg issues from excess salt build up and also from them just needing more 3-4th week flowering. you say you flushed but did you flush from the top through the rockwool as well?