Nutrient def?????

Hi everyone. Me need help. I've been growing for a few months now, so far so good, until now! I'm growing white Russian, its been in veg for 4 weeks now and has developed a rusty colour on the leaves in between the veins. This starts as milky white spots that develop into rusty spots that then spread across the leaf. This is only happening in the middle to older aged leaves. Plenty of new growth coming through quite happily. I have included pictures for diagnosis. I'm growing in rock wool slab in an NFT set-up using canna aqua. Currently veging under one 400w grolux. Nutrient levels and ph are spot on. Air is free flowing, not being forced in or out as of yet. I've had a look around and im thinking mg def? Any help would be.......... well yea, helpful!

if you ask me nd thats just if you ask, i thing you have a big case of bugs.

an Mg def. wouldnt do this, u would see the light green in between the veins. What nutes are you using and how much?

Once again I see a PH problem. These are classic signs of high PH most likely coming from the tap water. I'm sorry to sound like a one-hit wonder here and preaching the same line over and over but like I said earlier, most problems involving our plants stems from bad PH. Second cause for most problems is too much loving and third being natural (insects, disease, etc). All of which are controlable but only after a proper diagnoses first.

I'm growing White Russian right now too and know they're a hardy plant and should recover quickly once you find the source which I would bet on it being fixed once you either filter your tap water or use bottled water. A quick, easy and cheap test kit can be bought at any nursery and you'll be able to know for sure exactly what the prob is.

I'm using canna aqua veg, 3/4 strength. As for ph I've kept it accurately between 5.8 and 6.0 using a digital ph tester. Any more ideas welcome.:jointsmile:

Just to add to the previous posts, after pruning some of the worst affected leaves the problem doesn't seem as fierce but i have noticed that the top leaves are yellowing in colour. I must point out that there is a lot of healthy growth but this strange attack on certain areas of the plant is doing my head in. I've attached another photo if it helps. Also changed the nutrients today and added canna trace elements, appreciate any comments????