Yellow spots usually mean a magnesium deficiency, but for 7 weeks of flowering Im not really sure whether its worth sorting out. Most strains only take 8 weeks, with sativa dominant strains taking as much as 12 weeks, so I really wouldnt bother sorting it out. If you do want to though, just visit your local chemist and ask for some Epsom Salts. Theyre VERY cheap (£1 for a 500g tub), and last ages aswell. Use about half to a full teaspoon per litre of water to start with, and increase as necessary. Its usually sorted out with just one dose.

Edit: how did the MG ferts work? Ive been using 5-5-10 tomato feed and have now found some MG ferts the same as yours. Was it the powder or liquid fertiliser, and how much did you use per litre/gallon of water? Oh, and most importantly, did it work?