Light brown roots on Phalaenopsis

[estación seca]

That orchid food is acceptable. Fertilizer is the least important aspect of orchid growing. More important are air at the roots, proper light, proper humidity and plenty of water. Learn about those, and then it will be time to think about feeding.

If this is your product:
https://www.miraclegro.com/sites/g/f...100813_cfl.pdf
you can use a pinch per gallon (less than 1/8 of a teaspoon) at every watering.

It lacks calcium and magnesium. Unless your tap water has a lot of minerals, you should also use a calcium and magnesium supplement for your orchids. Use it according to the label. Don't mix the fertilizer with the cal-mag supplement in the same water; they can interact.