It could definitely be CalMag-related – the rust spots are a classic sign. But before upping the dose, check the pH of your runoff water to make sure your plant can actually absorb CalMag.
In soil, aim for a runoff pH between 6.2 and 6.5. Even if you’re feeding the right amount, a pH imbalance can block uptake.
Also worth checking: salt buildup in the soil or excess potassium can interfere with calcium/magnesium absorption too. If in doubt, a light flush and recalibrating your pH and feeding might help!
You’re on the right track – just dial in the details and your girl will thank you.