So, first off, you can dose vibrant AND a carbon source like vinegar. Vibrant’s website actually encourages carbon dosing while using Vibrant, since Vibrant is just a specific blend of bacteria the company developed, as I understand it. But if you’ve already got extremely low nitrates and your only issue is red cyano, I’d say cut back on the Vibrant dosing & don’t worry about adding vinegar. You could do a low dose of vinegar on top of the Vibrant dosing or use an alternate bacterial additive along with carbon dosing. Adding more flow to the areas cyano is developing would probably be best.
It seems like a lot of reefers get so caught up in achieving one thing or perfecting things that they forget the goal is balance & stability. Just be careful and patient when making changes.