I've tried many different cloning methods including hydroponic. It seems counter intuitive, but clones in soil, starting mixtures or pods need to be drenched to start, but after that they need to dry out, especially if they are under a dome. Otherwise they will rot/fail very quickly. Clones in starting pots without a dome will need to be watched carefully for wilting due to getting too dry in the first 2-3 days, so they'll need water a couple of times a day, but after that, they should start to be more self-sustaining and also be left to dry out so they will develop roots seeking moisture downward more quickly. I recommend using "Rapid Start" for quick root development. It doesn't take much and really does accelerate root growth, even on puny clones.

The bottom leaves of clones (and maturing plants) will turn yellow, that's normal. The tips of the clone leaves may also turn brown; these can just be trimmed off.