Hello madamadam14,
First, what you have made is a bunch of wick systems, not water culture systems/DWC systems. Lack of aeration to the roots is a common issue with your design.
Second, heat lamps wont work. Try florescent
lights.
Third, by your own statement they aren't wicking up enough water because you said the rockwool cubes are dry (quite possibly because the heat lamps are drying it out faster than it can wick it up).
Fourth, not only do you need to watch your water temperatures, but your air temps as well. Those plants have different temperature preferences.
Fifth, seedlings need high humidity. A clear dome will hold the humidity in, as well as still let the light in.