What is this?

Any advise is much appreciated

You might find what you're looking for here...

The plants are in flowering now. I'm thinking you may do best to feed it nutrients. If you're just starting out - maybe hit a garden shop for nutrients that treat the bloom/flowering stage.

Check your ph water level after you add nutrients. Water should be around 6.5

that leaf edge curling upwards is due to high heat in the grow space. you got to get the temp down to 75F or maybe a little less if you can. please take pics in white light to show color better.

I had the same problem once from heat stress what are your temps , how high are bulbs from canopy . What type of light/hood?

Heat stress or wind stress. Those would be my guesses.

Sisco said:

Any advise is much appreciated

Click to expand...

whole bunch of good pics here
https://www.icmag.com/ic/showthread.php?t=231387
calcium maybe? check out the 4th & 5th pics in the link...

By the chart I'd say early potassium ??

Can you take a picture is regular light?

If its not happening to all your plants then that plant or plants are in a hot spot get more air flow over the tops of your plants. Your room can be 90 consistantly and if you have great air exchange and circulation your plants will be fine. I may be wrong but I think plants grow faster than when they were in 85-90 degree temps consistantly with good air flow, than in constant 75-80. I know that goes totally against the grain and textbook but its just my experience.
Edit: Im not talking about adding Co2 either just natural fresh air.

heat and cal/mag deficiency. lower the heat and boost cal/mag, should fix itself easily

Those fucking charts are CRAP!
The way they depict things makes it WAY to easy to miss diagnose one problem for another....I hate those things....
Unless you really fuck up.....Micro nute def/overage is rare......Iron would be the one you might get first over all of them and that's because that one is easy to get "blocked" by mistakes......

The best way to actually "SEE" a problem and actually learning it in our plant of choice is to simply google for image's of Marijuana plant problems......Look at a LOT of the sites with them (by clicking on the pic and then the "visit page") and bookmark the best 2 or 3 for future reference!

Doc