5% every other week probably isn't enough, esp if things are bleaching. Sounds like your corals are starving for nutrients, especially if you aren't dosing anything. That is one of the important things that water changes do. They not only export nutrients, but they also import nutrients. A lot of people don't think of it this way but your corals are living animals too. They need vitamins, minerals, aminos, etc, just like regular animals (and people) do. Otherwise, they become unhealthy.
I do 10% week and still dose iodine, strontium, trace elements, iron, and amino acids, along with the standard alk, cal, and mg. You might opt for a $49 Triton test just to see what your parameters are, depending on the size of your tank. If it's less than 100g, just do a bunch of water changes, 50% or so and that will help you get caught up. Then figure out what you should be dosing to keep them healthy.
