another grow another problem!!

hi, im hoping I can get some help diagnosing this, some details first, ive got 10 incredible bulks, 2,amnesia, and 1 supersilver haze, they are all 3.5 weeks into flower, (expected 8-10 week for flowering), im in allmix soil, last pot up just before flowering, ph is allways 6.4 to 6.7, just feeding bio grow and bloom, following "old timers feed schedule" got to week 3 and gave some Epsom salt as recommended as a pre-emtive measure to deal with the deficiencys you can get with bio bizz, (though there was no sign of it)1 table spoon per 10 litres, that was on Saturday, checked them on sunday all good, didn't get to see them yesterday, went to see them tonight (tues) as its feeding time and noticed that on about 5 plants there are a couple of yellowing leaves, all of them are in the MIDDLE of the plants, it looks to me like its going inwards rather then outwards on the affected leaves, im torn between mb, and cal/mag but even on the worst leave its just yellow no rust spots or anything, the rest of the plants look great and no buds are yellowing (yet) , I know the plants in effect dying etc, and sometimes they yellow as they get nearer the end, but id have thought that would be a bit later on, so have I blown it by giving the Epsom salts? or perhaps not enough?? what do you think,
any help is apreciated

I hope someone gets back to you with a definitive answer as I'm experiencing the same kind of yellowing right at like 2.5 weeks into flower and was just about to go out and get some epsom, I haven't been using a whole lot of nutrients though so I understand why it is happening to me. Have you tried flushing? Thats always the go to recommendation around here to fix anything. There could be a build up of salts causing a lock out.

begining of to much P

A pic of the whole plant would tell me more though!

thanks for the replys, cant get more pics till tomorrow now, should have thought of that!! if you've got time tomorrow ill get them put up,it realy is 2-3 leaves around the middle, ive been feeding 1ml per litre of bio bizz grow and 2 of bloom, was gonna up the bloom to 3 this week but held of tonight, as far as build up goes I only repotted 1week before I flipped them, and with the nutes being natural/organic I would not expect that, but do take it on board,