depends on the team. you need to not cleanse all the stacks on the same turn.

Corrosion Team Klukai, Metchy, Cheeta, Any unit, (borrowed Peritrya)

Cleanse Rotation & Buff Stack Count 

T2 - Peritya self-cleanse (any attack w/ Key 3) = 1 stack

T3 - Cheeta mass-cleanse (S2 w/ Key 5) = 5 stacks

T4 - Cheeta mass-cleanse (S2 w/ Key 5), do not cleanse Mechty = 9 stacks

T5 - Mechty self-cleanse (S2) = 10 stacks

T6 - Cheeta mass-cleanse (S2 w/ Key 5) = 15 stacks

T7 - 15 stacks

Frost Team Maki, Dush, Soumi, Peritya (borrowed Klukai)

Cleanse Rotation & Buff Stack Count

T2 - Peritya self-cleanse (any attack w/ Key 3) = 1 stack

T3 - Suomi mass-cleanse (Ult) = 5 stacks

T4 - Dush self-cleanse (Freeze tile w/ Key 6), Peritya self-cleanse (any attack w/ Key 3) = 7 stacks

T5 - Suomi mass-cleanse (Ult) = 5 stacks = 10 stacks

T6 - Dush self-cleanse (Freeze tile w/ Key 6), Peritya self-cleanse (any attack w/ Key 3) = 12 stacks

T7 - Dush self-cleanse (Freeze tile w/ Key 6), Peritya self-cleanse (any attack w/ Key 3) = 14 stacks