yellowing leaves @ week 3 flowering questions

If they come right off when you give em a lil tug then your good.

 

It's natural for older leaves to die off

 

Increase your Magnesium and your Sulfur levels with a little Epsom Salt. 1/4 tsp in 5 gallons of solution adds about 10ppm of each to the mixture, which is just enough of a boost to help keep those elements competitive.

Watch your calcium levels at this point forward in the grow. It may also benefit you to collect a little extra run off the next few times to ensure that an excess of one element is not drowning out other elements. Feeding more when you already have too much of something will only compound your issues. Keep the levels fairly steady and just get that runoff. Concentrate on stopping the yellowing as your plants are about to hit the first two weeks of really important flower development. Stress during these periods will dramatically decrease your harvest weight.

So a pinch of Epsom Salt, a little extra runoff, and if you have some Liquid Karma around then you could definitely run that at up to 8ml per gallon right now to add a little extra potassium and to help keep production rolling forward. If you're into foliar spraying then you could do a pinch of epsom in a bottle of water with a drop of biodegradable dish soap, like Ivory, and spray the underside of your sicker leaves with it and that could stop the necrosis from happening at least. Always spray just as the lights come on, and just a little bit. Only twice per week would make a difference if your issue is what I think it is.