Yellowing Lower Leafs??

I am doing a grow in a 3X5 closet. I have several plants all seem do be doing well under 400w HPS. I started flowering 3 weeks ago and switched from General Hydro three part to SBA Super Bloom A and B. My babys are pretty tightly packed together and I am noticeing some of the lower fan leaves are yellowing and falling off. I think this is normal during flowering and when switching to flowering nutes. Just wanting to get another opinion. Thanks

I am about 2 1/2 weeks into flowering and I'm getting the same things. I assume it's normal, it doesn't look bad. Just looks like the cycle of life. Older, lower leaves are being sacrificed to build the new growth and to give fuel for the flowering.

If you switched from a high N fert to a high P fert for blooming then the likely causes is nitrogen deficiency,
Feed them with some veg nutes or urine, fish emulsion, or bloodmeal, they should respond in about two days if this is the problem.

Same things happening to me, about day 20 lower pairs of leaves started yellowing, and got knocked off, ive lost atleast 3 pairs of single leaves so far. I didnt even change anything, except add abpout 60w of cfl.