Yes, I also strongly suspect that you are overwatering by watering too often. What is likely happening is that even though you are giving a small amount, intending to just water the top surface each day; what is not being used immediately by the top spreader roots just below the surface, is then dropping down to the bottom and adding to the the pool of stagnant oxygen starved water sitting in the bottom. Watering just the top is a valid strategy whilst starting out a seedling, but as soon as the plant's width has spread out to 1/3 to fully the width of the container, it is time to fully water the container to runoff each time, and then wait for the plant to use ALL of that water before watering again.
The waiting is what you are not doing and why your plants are shutting down... they are simply getting too much water and the lower roots, not being able to ever get oxygen pulled down to them, are going into survival mode.
I would like you to read two pieces of mine... both referenced below. The how to water a small plant in a large container article will explain the top surface watering method and when that is appropriate, and the main article will explain how you need to water from now on, trying to establish the wet/dry cycle that our weeds love so much.
