Do you need CalMag supplementation with MSU?

[NewBloom]

I first started fertilizing with an MSU fertilizer (13-3-15 8Ca-2Mg). When the MSU finished, I switched to Dyna-Gro's Grow 7-9-5 with the calcium magnesium being 2 and 0.5 respectively.

Lately, I've been considering adding cal-mag or Epsom salt to my feeding program once a month. I would use it one week a month without adding any other fertilizer. Some of my rescue phals have new leaves where the growth just stopped. Do you think the 2 Ca and 0.5 Mg in the Grow were too low and created a deficiency?

I will switch back to MSU when the Dyna-Gro runs out. Is Cal-Mag supplementation necessary when using a MSU fertilizer?

I also have crushed oyster shell for my cyms. Would using that take the place of a liquid cal-mag product?