In my experience the presence of algae, moss and mold are real danger signs. Drosera seedlings cannot compete with these other species, especially in the early stages of growth.
Once the problem starts, it is difficult or impossible to deal with. This is why care must be taken on the preventitive level, esp. when sowing seed.
These competitive species arise when there are micronutrients available for them to exploit. Once bluegreen algae and cyanobacteria get a toe hold, they fix atmospheric nitrogen into the mix, and the process accelerates. Careful washing of the sand used in the medium will go a long ways in prevention of the problem. Rinse the sand before you use it until the water runs clear. I also use only peat that has weatered outside where the rains leach out any nutrients that may be present. I keep my peat in a bin with drainage holes, and the seasons rains does the work for me. I find that droserae prefer older peat.
Another alternative method is to sterilize the mix with heat, but I have not used this method much. Others report excellent results doing this, so it is a consideration.
Finely milled LFS is also a good germination medium. If the moss is living, it should be very well milled in a food processor. The low PH of this medium is naturally aniseptic, and I have yet to meet a CP that would not grow in LFS sphagnum.
In all events, a ounce of prevention is worth a pound of cure, and cleanlieness is next to godlieness in any method of CP propagation.