Please help with leaves problems asap

Hi guys another post regarding this seems to be getting worse have flushed today I have leaves that are yellowish with brown spots the tip goes brown curls up and eventually half the leaf turns brown and crumbles I noticed when I looked at the leaf it was fine yet when I held it up to light I can see the brown spots within the leaf I'm getting very concerned pH is 6.5 .growing in soil temp is 26 degrees Celsius I have been LST since clone and also noticed hundreds of spring tails in the soil when watering I have read these are good to have but could these be causing the problem thanks in advance

Over care is the number one killer. If you lost a leaf or 2 ..... it happens. If its affecting your whole plant....that's different. If a leaf starts to die, or gets damaged, was affected by a short bout of nutrient loss....whatever the case may be.....trying to correct your conditions based on just a few leaves will almost certainly lead to killing the thing. Not to mention...it wouldn't save the leaf even if you could. Let old growth die. Monitor your new growth more closely. Pot plants are hearty! They can do with some neglect. It may do you good to let that soil dry out. The dryer it gets the more oxygen it pulls to the roots. Be sure to do this periodically. then water deeply and repeat. it causes amazing growth. As for your pictures and such....there's not really enough info...but i don't even think you have a problem.

That looks like a Potassium deficiency. Feed it something with some K in it.