What is causing this on the leaves?

I agree with my growmie that it's calcium deficiency BUT the question is why... it might be that it's just deficient, but you're not giving it too much nitrogen (Tiger Bloom contains SOME but not enough to cause a calcium lockout) ... so I would ask what your PH is since I don't see that info in your diary. Growing in soil, you need the PH to be between 6.2 and 6.5... preferably the lower end but NOT lower than 6.2... if it's lower than that, you can give it all the calmag you want and it won't help the problem because the plant just simply won't be able to absorb it. So check your PH before adding the calmag! Good luck!