Leaves on interior lower and middle plant turning yellow and falling off. Heat and recently changed feeding schedule. Should I switch back or just heat?

Gotta agree with InspireMe, sounds like a little nutrient lockout. Only guessing that because I have the same issue, to a much lesser degree, and my medium is at an irritating 7.0 with some spikes. The plants I have showing yellow leaves just Ph'd the other day at 7.2, the ones without yellow still Ph'd at 7 even.

Hey mate, I had a look through your diary and I think it could be related to your ph. I noticed that you ate running at 7.4. I'd try and bring that down to anywhere between 6.0 and 6.8. They may be struggling to uptake the nutrients they need. Hope this helps 🙂