The plant IS nearing the end of its life cycle and yellowing of the low leaves is normal.
You say there's a chance they could be getting cold at night and cold soil combined with any pH issue you might have will cause symptoms exactly like you are seeing- a multi-nute lockout, in your case N, Ca, and S are pretty apparent. The N is a no-brainer since your bloom fert doesn't have any, and feeding once with grow fert was a good call. Next time, use your grow fert for the first 2 weeks of flower so you don't have to give any later. It's better that way.
If the plants are on a cold floor, put them up off it. If you are already seeing some amber, you're really close to harvest anyway.
You're going to want to give a good flush as well. Some of what you describe sounds like you've got a salt buildup in the soil. Flush well and feed immediately with a balanced fertilizer- that grow fert you've got would be appropriate if it contains micronutes- and then on the next watering return to your regular flower fert.
Lastly, keep on top of your pH! Excess fert residue in the soil will eventually cause problems.