Leaf Curl..day 30 flower..Nute burn or Def....???

[crystal_palace]

OK, im on my 5th grow... All grows have went well and ive always ended up with top quality smoke.. All my grows have been organic in soil under a 400w HPS. I always end up with leaf curl and burnt crisp tips on just the bigger oldest fan leaves about halfway through flowering... It never seems to affect the buds or small leaves around them. It just starts as a slight curling of the entire fan downward, Then the tips kind of yellow, then brown and curl up a little, just at the tip. Finally the leaf will be completely yellow and die and fall off. This does not affect new growth and there is no yellowing of new leaves or in the buds. Im not really too worried about it as i always end up with good smoke and all. I just wondered if anyone had any ideas as to what it could be? It cannot be nute burn or over fertilization if the new growth isn't yellowing, right? thats my main concern; and since new growth is healthy i cant see how that could be the issue. I thought maybe my soils lime was being used up by that time and the PH was just getting a little low. I added a little lime to my containers by scratching it into the first 2-3 inches and then mixing a little up in water and watering with the lime. It may have helped a little, but the curling and browning tips on the older fans is still happening like always... I add cal-mag to my water because i water with about 1/4 tap water that i leave out for at least 48hrs. and then 3/4 reverse osmosis water from grocery store that i add the cal-mag too. I fertilize with some Bloom fertilizer called "rainbow mix" that i mix in 2 weeks into flowering its npk is 1-9-4 i believe. I scratch that into soil first 2-3 inches. Then i also fertilize with a liquid fertizer organic all purpose bloom made by botanicare specially for soil. I use that about every other watering at half strength. It seems to me that the plants almost need more food. The bottom larger fans on a couple plants are really yelowing quick and i know and can tell thats a N def. But i also know that during the last half of flowering a N def. isn;t a problem. Any thoughts would be appreciated. Sorry no pics. Mainly just making sure im not over fertilizing and looking for some opinions on what else this could be.....

[Tha420]

Pictures?

[crystal_palace]

i said sorry for no pics...... I just want to know if there is anyway it could be nute burn? Im assuming not because im using low strength organic nutrients and only older fans are being affected....

[TexarkanaTim]

Its common to get leaf yellowing during the end stages of flowering. As long as you are getting good production, I wouldn't worry about it.

[makinmoney21]

iv read that it is normal during the flowerin stage that that happens the plant is using all the nuts for the flower ..