6 weeks into flower leaves burning

Hi my plants are 6 weeks in flower under 600w hps light they were fine growing bud until last night when I went in to water them all the top leaves were burnt to a crisp.Now they dont have much leaf on the top.I have them on the go since January and I'm going to cry if they dont work out.I dont understand why they didnt burn from the start and all of a sudden went from healthy to burnt to a crisp there was no sudden heat wave for them.will they push out some more leaf at the top or is it to late in the game for plant to produce green? Im going to post some pictures to see what the experts opinion is on this subject.Also Im a bit worried on when to harvest them as the seed packet says 55days flowering and another person told me on this site they would take up to 11 weeks flowering as they are hybrids any in put is appreciated thank you.

Even though the plant's are at 6 week i would flush the plant's through with a small ammount of nutrients but mostly water.But make sure that this burning has not been caused by clumsy watering because i have seen several grow that the leave have had severe burn's through nutrients been spilt on foliage.Then leave them to dry out beforere introduceing any full strenth feed.Pull of all the worste effected leave's has these could lead to a mould so pull of the realy bad ones and cut the tip burns back with scissors to the green part of the leave.But in future build up to a strong feed it looks to me like you have introduced a too strong feed too early.or the ph is of the the ricktor scale

man take decent/clear photos if you want help.

Thanks for replying and sorry about the pics bad camera.Im using hesi bloom complex and it was working fine i mixed it up wit 10l water as instructions said to do
I just used the last bit in the end of the drum 3 days ago.Could it be from the bloom building up at the end of the drum and then when i used it it overdosed them and now its taking effect.Im very careful on watering as my mate ruined his babies from spraying leaves and light reflecting through the water.I will flush them tonight and see how they get on.They are 6 weeks in flower now but not even an ounce on a plant my mate said that aint good.Do they bud more near the end as he aint an expert he wouldnt know.I have 3 different types BIG x NORTHERN LIGHTS,YUBOLT 47,and STRAWBERRY BLUE,all hybrids.

A few leaves look like they are bleached they are yellowy green should I cut them back too or should i flush and take the burnt 1s off.