I am looking for a liquid that floats on water that will prevent the water from freezing (or at least slow it down). The application would be a small area (less than a square foot). It has to be non-toxic as I do not want to harm any critters. Thoughts???
There are oils sold for swimming pools to slow or stop evaporative cooling . That would be a problem for air breathers like mosquito larva. I don't know anything about it because I went with 1" thick Styrofoam panels. That is what I currently have on my pond ( 10' X 5 '), works very well .I cheat a little and have 150 watt aquarium heater in the 700 gallons. My pond is currently 59 F while nearby open water is 49 F. For your tiny area the Styrofoam is fine leave about 1/2" on all sides for air . On the other hand why not do the obvious and put in a 25 watt ( if they make them that small) aquarium thermostat/heater ?
A possible more natural solution allowing continuing oxygen exposure, use a layer of leaves resting on a frame (say wood branches).
Supporting related comments can be found here, to quote:
Leaves can be used to insulate plants from cold weather. To provide protection for plants, including container plantings, circle a plant with wire fencing. Then, stuff leaves inside the fencing all the way around the plant...Moreover, if you have a root cellar or storage basement, you can use dry leaves to layer your vegetables in, rather than using sawdust or newspaper. This should allow them to be stored through the winter.
No guarantee of success, but perhaps better than being completely exposed.