How to check player inventory for items/blocks with custom tags

Howdy, I have created a custom tag which contains over a dozen blocks, I have called it: heavy

What I am trying to do is have minecraft check if player has said tagged blocks tagged as "heavy" in their inventory and apply a slowness effect to them.

I am not sure where to begin, all I know is I want.

"If player has blocks with tag "heavy'

do: Apply potion effect: Slowness to player

I've found several things I think I can use, I'm just unsure of how to use them in a way that works for what I'm trying to do.

EG: "Has ___ In inventory"

"Is __ tagged in item tags as ___"

"Is __ tagged in block tags as ___"

Also, would the on player tick update work with this, or would it cause severe lag?

Any help is greatly appreciated, 

Thank you