I found some osmocote plus which contains ,

It is a 15-9-12 for N-P-K

slow release is

12.6% nitrogen,

7.6% phosphorus,

10.2% pottasium

1.6% Calcium .

6% magnesium

3.4% sulfer

0.0017% boron

0.38% iron

0.017% molybdenum

0.051% manganese

0.019% zinc

My question is, with using this with all the micronutrients included would i still need to use gypsum in al's gritty mix?

Also i am curious as to how much to use for a 24" container (approximately) since it says 3 tbs per 4 square feet i believe.