You can also make a general expression:
. If a creature gains a|b (positive ot negative), the creature gains an aditional -(a+b)/2 | -(a+b)/2
For example, if a equilibriumed creature gains a 2|4 chaos power buff, the final result of the "buff" will be 2-3 | 4-3 = -1|1
Now you must decide what happens if a+b is not multiplier of 2, because as you know -(a+b)/2 has a decimal term. In other words: round up or down?
Remember, the simpler the better.