i final got to the bottom of my plants problem. it was a mix of a number of things - root bound pots, magnesium, iron, zinc & nitrogen deficiency.
i plunged a 6mm dia., 1 meter long rebar into all the pots to loosen up the soil & break up the roots. i tried it on 2 plants 1 evening & the next morning the plants had improved noticeably. so that evening i did it to rest of the plants. it took some doing in certain place to get the metal bar thru the roots, they were packed tight. i then ripped down along the top of the soil about 3 inches deep, cutting / ripping the roots & fluffing up the soil. i found that by letting the plants sit for about 12 hrs without water after ripping the roots & then fertilizing with a mix of flowering fert & a half strength veg fert gave the best results to their recovery.
my nearest grow shop is over a hours drive, i went down today & the woman there gave me her opinion of the leaves i brought her. it coincided with what the people on the forums said it might be, the above mentioned deficiencies. so i bought a mix of locally made bat guano with all the goodies the plants need, including a root oxygenation, a bacteria to re-establish the good bacteria & a bunch of other good / neat things.
i had mistaken the burnt leaves as a fert over dose & had flushed the pots too much causing the other deficiencies. growing in pots is a world of difference than growing in the ground.
thxs for you help