Anyone got any ideas on what’s going on with thi...

Hey there Luv2grow, you're totally right ! It's a textbook calcium deficiency ! you can tell by the "rusty" small spots appearing on the leafs. Problem is uptake efficiency by the roots is only 15% so that means it's gonna take a while to show an effect. Keep doing what you're doing and the problem should stop spreading and the plant should recover within 10 days to a week. If you want quicker results consider using a chelation agent : this breaks down the nutrients so it's more easily absorbed by the plant try any of these : go bio with enzymes, amino acids, humic or fluvik acid, or synthetics like 0.3% HydroChloric Acid. Hope this helps ! 🚀