Weird discolouration on all my plants

[chicken_phat]

Hey, I noticed some weird colour changes on the top set of leaves on all my plants (5 varieties, all affected). I have no idea what's going on. Is this bad? How can I fix it?
 

 
 

 
 

 

[megahot]

When was the last time you fed them? It could be an NPK def.

 

[chicken_phat]

When was the last time you fed them? It could be an NPK def.

 
The potting mix that they're in has a slow release fertilizer, so I assumed that was enough. What type of ferts should I be giving them? 
Last time I watered them was probably 1.5-2 weeks ago.
 
This is the potting mix I used: http://www.canadiantire.ca/AST/browse/2/OutdoorLiving/Garden-Care/GardenFertilizers/PRD~0594405P/Miracle-Gro+Potting+Mix.jsp?locale=en

 

[megahot]

So, Im sure they need to be watered, if its been that long. When did you pot them up in that potting soil they are in? Im betting they need to be fed. I feed my plants with Dynagrow. Just a basic fert will work, although I dont like Miracle grow.

 

[chicken_phat]

They were potted up just over a month ago. There are two plants per pot, and each pot is 10 or 11 gallons. I'll water them and pick up some fertilizer tomorrow then!

 

[pshngo]

looks like sunburn. cant see from my phone. is it in the veins of the leaves or across the tops of the bumps on the leaves?
?

 

[chicken_phat]

looks like sunburn. cant see from my phone. is it in the veins of the leaves or across the tops of the bumps on the leaves?
?

It's running through the veins mostly.