what can i expect yeild wise?

here are my girls. 3 blue mystic and one auto bang. they r under a 400 watt MH and surrounded by mylar. i have been feeding them once a week with super bloom and tiger bloom and they seem to love it. but i do have some yellowing one my biggest plant and everyday another leave stats yellowing. despite the yellowing the buds and the overall plant looks great. is the yellowing because it is a natural process or a def.? i dont know how long they have been flowering. i startes growing them mid december from seeds and vegged about a month give or take a week. what will the yeild be approximently? and any tips when it comes to harvesting because this is my first successful grow. thanks!

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Also the buds are supposed to have a blue hue to them and i was wondering when does this happen or do i need to add something to the water for the color change?

let the plants continue to mature and eventually you should see some blue hues, but the color might not come out until after the buds are dried and cured.