does candy stack with a con set?

if i eat red rock candy and use a con set will they stack?

Cons will stack unless there is a cap on certain bonuses. For example, speed boosts will not stack beyond 33%, IAS will not stack beyond 33%, etc.

For the speed boosts there are hard caps at the top but when an opposite effect will slow you down, for example by 50% then you will get the full benefit of the stacked cons.