The same problem for the last 3 grows please help!

I read threads. Uncle Ben's sticky thread somewhat answered my question i think? I have a kandy kush, white widow, and pineapple express going right now. I had Kandy Kush the last 3 grows with this same problem. My plants are doing excellent till about 2 months into growing. This grow it showed now, which is the first week of flowering. The leaves starting at the bottom discolor and dry up i'd say. I am using subcools super soil that is not the revised version. I didn't see the revised version till after i made that batch awhile ago. I'm almost positive it's overfertilization. am i correct? If so could i leach them without draining all the nutes out? Thanks for the help. Here is some pictures.

Rootbound because pot is 3 sizes too small which in turn encourages huge salt build up (by now its had a few feeds), in other words repot now and add perlite to stop drooping and shock after transplant. As you were thinking- rootsystem stress.

Oh dam will it delay my flowering alot? what size pots should they be in? Thanks for the input. I'm not to the point yet i could help other people yet. i'm still learning.

what kind of nutes do you give for flowering?

None, i made tga subcools super soil. could it be over fertilization to or no? Thanks for the help.

to bo honest it looks like phophrous deff you have them in 5 gal buckets so i dont think it would be root bound i have never had root bound and i use 5 gallon buckets. the bottem leaves falling off sounds like root bound the browning on the top leaves looks like phophrous def.

Thanks for the help. You were right about the phosphorus deficiency, But that was because my ph was low. I'm not a 100% sure. I bought the fastest acting lime you could get at lowes. My plants have definitely not gotten worse. They are at least the same, maybe the growth is going a little faster. As for the phosphorus deficiency, Will the super soil still be potent enough to resolve the phosphorus deficiency, or should i add an organic phosphorus supplement? Thanks for the help?