My third plant(Blue Cheese) at 4-5wks was watered on Tuesday with
wk 3 Grow @ 50% (0.5 gal) till just visible leakage on tray. Today, Friday, I am noticed a few oddities.
1) Some of the leaves seemed a bit floppy
2) Lifting one leaf off of another that were in contact revealed some moisture
3) There is leaf curl (upwards on many leaves), predominantly towards the top.
Conditions:
Temps have been between 80-87degF
Humidity has been hovering at 50-58%
Lights have not been closer than 24 inches as this plant sits 6in + lower than the two blooming plants
The pot seems light, but maybe not quite as light as the other two plants that I recently fertigated
POSSIBILITIES OF CAUSE
1. Too much marijuana fertilizer
The most common cause of marijuana leaf cupping aka leaf margin rolling, leaf margin burn, and leaf tip curl/burn is overzealous use of marijuana plant food. In relationship to factors such as marijuana plant vigor and rate of growth. Leaf burn is often the very first sign of too much marijuana fertilizer.
A hard, crispy feel to the marijuana leaf frequently occurs as well, as opposed to a soft and cool feel of a happy pot leaf. Back off on the amount and/or frequency of using marijuana fertilizer. Too much marijuana fertilizer can also burn the roots, especially the sensitive root tips, which then creates another set of problems. Note - as soil dries, the concentration of the remaining salts rises further exacerbating the problem.
Thoughts: @ 50% of wk3 fert, I do not feel that I have over fertilized this plant. Leaf color is far from the dark green of my other two plants and had started out almost on the yellow side earlier on.
2. High Heat
The marijuana plant is losing water via it’s leaves faster than what can be replaced by the root system. The marijuana leaf responds by leaf margin cupping or rolling up or down (most times up) in order to conserve moisture. A good example is reflected by the appearance of broad-bladed turf grass on a hot summer day, high noon, with low soil moisture levels - the leaf blade will roll upward/inward with the grass taking on a dull, greyish-green appearance. Upon sunrise when moisture levels have returned to normal, the leaf blade will be flat. Lower the heat in the marijuana grow-op and concentrate on developing a large robust root system. An efficient and effective root system will go a long way to prevent heat induced pot leaf dessication or marijuana leaf margin curling. One short episode of high heat is enough to permanently disable or destroy leaf tissue and cause a general decline in the leaves affected, which often occurs to leaves found at the top of the cannabis plant. The damaged pot leaf (usually) does not fully recover, no matter what you do. Bummer in the summer. One can only look to new growth for indications that the problem has been corrected.
My Thoughts: This is plausible. Thought not excessive hot this plant may not be as tolerant, who knows
3. Too much light
Yes, it’s true, you can give your marijuana plant too much light. Cannabis does not receive full sun from sunrise to sunset in its natural state. It is shaded or given reduced light levels because of adjacent plant material, cloudy conditions, rain, dust, twilight periods in the morning and late afternoon, and light intensity changes caused by a change in the seasons. Too much light mainly serves to bleach out and destroy chlorophyll as opposed to causing marijuana leaf cupping, but it often goes hand-in-hand with high heat for indoor marijuana growers. Turn down the time when the lights on in your marijuana grow room. If you're using a 24 hr cycle, turn it down to 20 hrs. Those on 18 - 6 marijuana growth cycle can turn their lights down two or three hours. Too much light can have many adverse effects on marijuana plants. Concentrate on developing/maintaining an efficient and robust root system.
My Thoughts: Light schedule is at 18/6, 100% Veg, 100% Bloom. Can't rule this out
4. Over Watering
For marijuana growers using soil, this practice only serves to weaken the root system by depriving the roots of proper gas exchange. The marijuana plants roots are not getting enough oxygen which creates an anerobic condition inducing root rot and root decline with the end result showing up as leaf stress, stunted growth, and in severe cases, death. Over watering creates a perfect environment for damp-off disease, at, or below the soil line. Many times marijuana growers believe their cannabis plant is not getting enough marijuana fertilizers (which it can't under such adverse conditions), so they add more marijuana fertilizers. Making the problem worst. Not better. Often problem 1 and 4 go together. Too much marijuana fertilizer combined with too much water. Creating plenty of marijuana plant problems.
My Thoughts: Gut feel is that I am definitely not over watering, and roots are not in soil.
5. Not Enough Water
Not only is the marijuana plant now stressed due to a low supply of adequate moisture, but carbohydrate production has been greatly compromised (screwed up). Step up the watering frequency, and if need be, organic marijuana growers may need to water from the bottom up until moisture levels reach a norm throughout the medium. One of the best methods in determining whether a marijuana plant requires watering is lifting the pots. The pots should be light to lift before a water session. After watering the marijuana plants lift the pots to get an understanding how heavy they've become fully watered. If the pot feels light to the lift - it’s time to water. Don’t wait until the soil pulls away from the side of the pot before watering. And of course, leach, once in a while to get rid of excess salts. These are the five most common problems marijuana growers encounter when growing cannabis. Correcting the problems early will save the marijuana plants, but may reduce overall yield. With practice and experience these problems are easily overcome which will then enable the marijuana grower to produce fantastic marijuana plants. With heavy yields.
My Thoughts: I may be leaning towards this scenario and was prepared to go down this path at 60% wkk3 Nutes, until I decided to allow for your experienced advice!
So, what say you, @Mañ'O'Green 
