1st grow problem, poss nute issue need solution

Hi All,
1st off thanks to everyone who contributes to these forums they are\have been and will be a huge help +REP to all!
long time toker, 1st time grower so be gentle!
i have an issue and thought i would ask help from across the pond.
started flowering 19/10 so currently 5 weeks'ish in
the 3 ladies are fem'ed AMS from greenhouse vegged for roughly 10 weeks, in soil (john innes 2, a kind of all mix) repotted 4 times and now residing in 10" pots (sorry dont know the gallon'age, but roughly 1.5) started nuting on week 1 of flower using bio bizz grow and bloom following 3/4 strength of schedule until last before watering (last being straight water) where on being advised that they looked N Def doubled grow for 1 off feed.
now they look nute burnt (most leaf tips brown) and i still have the same sort of prob that they look and have done since 5 days into flower N Def.
symptons (see pics) are most lower fan leaves yellow'ed an dropped off and older growth yellowing, bud leaves look ok, doesnt seem to be affecting the bud growth but am still losing leaves. thepheno 3 side comp.jpg double stength feed only looks to have burned them so here i am!
had very minor mite issue 2 weeks ago treated using nite, nite (b'stard) spidepheno 3 bud comp.jpgr mite all clear now
current setup
250 hps son agro
400 hps son t plus
extration rhino filter with prima klima 5" 240/350m (running 240 with goopheno 1 above comp.jpgd negative pressure) venting into hall
in 1.2x1.2x2m cheap mylar tent
input 4" inline TT from open window
various fans (clip and oscillating)
dapheno 1 comp.jpgy temps upto 26.5C
night temps 19C
last run off ph'd @ 7 (litmus paper, am saving for pen!)
all suggestions gratefully received
thanks all
GG

pheno 2 side comp.jpg
 
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