Ask Mr. Smarty Plants

We’ve recommended Prunus caroliniana (Cherry laurel) for privacy fences before, but never on a balcony; an interesting concept.
Mr. Smarty Plants thinks you have two problems to deal with; one is some sort of insect that is eating the leaves, and the other is that you are perhaps drowning your plants.

  Follow the link above to the Native Plant Database page and scroll down to:
  Growing Conditions
  Water Use: Medium
  Light Requirement: Sun, Part Shade
  Soil Moisture: Moist
  Cold Tolerant: yes
  Soil Description: Moist, deep, loamy, well-drained soils. Clay Loam, Medium Loam,  Sandy Loam, Sandy
  Conditions Comments: Likes the moist, well-drained soils of its natural range. Prolonged saturation            can cause root rot, particularly in clay soils. Shallow, nutrient-poor, rocky soils can cause chlorosis and   heat stress.
There are two key pieces of information here:”Water Use: medium”, and “well drained soils”. 

Watering twice a week may be just too much water. Try letting the surface of the soil become dry before adding more water to the pots. This link from Naturehills.com has some hints about watering plants.

One approach to getting rid of insects is to use insecticidal soaps. This link from Colorado State University Extension has some information you can use.

To get help with identifying the pest, contact the folks at the LA County Cooperative Extension Office of University of California Agriculture and Natural Resources.