I’m not sure if it’s a nutrient lockout or if I have a pest issue. If anyone could offer advice it’d be much appreciated. Thank you 
That looks like a micronutrient toxicity to me, maybe Boron. Do you know what your water quality is like?
Source: International Cannagraphic Magazine Forums https://share.google/d7AY3yJ44hgi7pMMj
See this look like cal. Or mag.
Yeah doesn’t look like that, my pic is apparently Boron deficiency not toxicity.. 
And yes it looks a bit like Cal def, that’s what I’d heard Boron toxicity looks like too but not according to that, and don’t think is OPs issue..
Water quality is first thing I’d check
What is your medium? Do you amend it?
If no amendments, what nutrients are you using and at what strength?
What is the EC and pH of your runoff?
Attempting to diagnose without first having this knowledge is just guessing.
Here is my advice. Cannabis plants need specific nutrients at specific times of flowering and you’ve got to hit these needs at the right times. It’s fairly easy once you figure it out but it’s one of the hardest things to figure out( for me)
Weeks 1-3 keep the nitrogen or grow formula even though it’s flower. You can do half and half or work your way up slowly. Like 75% grow and 25% bloom for week one and then 50 50 on week 2 and then week three 25% grow/nitrogen and 75% bloom and then week 4 you drop the nitrogen. They need nitrogen for the stretch and transition. It’s not just like flipping to 12/12 for the plant like it is the lights.
This is the most important week In my opinion.
Week 4 and 5 the plant desperately needs cal mag. It’s very important to hit this mark. If you don’t, then the rest of flower will struggle. This is one that you can’t miss. The weeks precious and the weeks after can be corrected or at the very least it’s not detrimental if you miss early and late flower feed compared to the plants need for cal mag at weeks 4 and 5. Calcium is the building block of plant cell walls. Which means they are a key building block for the buds and flowers. Without it, the plant will steal it from the leaves and you will have necrosis and leaf loss which can affect yields and over all plant health.
Weeks 6+ is when you’re hitting the pk. (Potassium and phosphorus)
At this point you can just kind of ride it out. Most of my nutrients still have nitrogen even the bloom nutrients. So continue the bloom but add extra pk which is normally a flower booster or something. It’s not needed but at this stage, your plants will eat more potassium and phosphorus at this stage.
I might be able to find the chart. It shows which nutrients are most needed at which time and I remember being surprised at the need for calcium and magnesium at weeks 4 and 5 and it’s the most needed at that time. I can’t think of any other point that it’s more important than nitrogen or whatever ya know?
Simplified version.
Weeks 1-3 keep the nitrogen
Weeks 4-5 cal mag
Weeks 6+ potassium and phosphorus
Obviously still feed how you do because all nutrients are different and all feed schedules are different but if you remember that your plant still needs nitrogen for the stretch and cal mag for mid flower and potassium and phosphorus for bulking and ripening. you can avoid alot of distress during the flower stage.
Hope this helps! Willing to answer questions if need be
Possibly pests. Spider mites or thrips possibly. The white marks on the leaves are what I notice.
It looks like your plant is having a cal mag and then phosphorus deficiency. Are you like week 4 or 5?
It could all be a ph issue though. Certain ph won’t let certain nutrients be available
Based off picture I think cal mag for sure. We use Oily Can. It has humic acid and sulfur. No nitrogen. I recommend it. Not sure about bugs. I didn’t see anything indicating bugs. Another recommendation check your ph. Make sure to give them good ph water. Depending on your medium live soil 6.7-6.0
Coco coir perlite. You can ph 5.8 up to 6.4. Hope this helps. If you suspect bugs grab some yellow sticky traps and put the around the plant. Take Care
No such thing as a “Cal Mag deficiency”. I don’t see pest damage or Phos def.
While it looks a bit like Calcium deficiency I really don’t think it’s that as it’s not happening to new growth and Calcium is an immobile nutrient, it’s obviously not Mag def.
A full picture of the whole plant and feed info would help. Really looks like a water/micronutrient issue to me, low pH can make micros too available but you’d usually see other issues first.
What ph and grow medium u using
Also another thing. How’s your water source. Chlorine and chloramine will damage your plants similarly to calcium and mag defs
Thank you for the detail. It could be the water source because I’ve been using tap with ascorbic acid the get rid of the chlorine and I haven’t been adding cal mag because of the tap water having heavy metals in it. But I also checked my run off and it was at 2100 so I flushed it back down to 1200. If that doesn’t help I’m going to switch to purified water.
Happy frog on top ocean breeze on bottom and fox farm trio
Ph 6.5 sorry forgot to add this
Make sure to let tap set out for 24hs but that only helps for chlorine a little bit. You may have some stuff in there that will not gas off. Invest in a ro filters. Always add some cal mag to your water. These plants love it. Ph seems fine at 6.5 but you can let it swing a little to unsure different nutrient uptake. Good luck my friend. Take Care
Just to clarify:
Your PPM was 2100?
Isn’t that like 4.2 EC?