Evaporation.
evapouration
It will cool down water temperature when by melting down AND it will lift up the water level in the aquarium
The fish are drinking it. Get rid of the fish
You need to get a water pump and filter for the aquarium at a pet store.
Because the fish need the enough amount of water every day of their lives
Do water changes, and use aquarium salt at around 1tsp per gallon
the water level would sink. Anything that sinks into the water would cause the water level to sink
There should be a line indicating how far they go down in the water
You can do a water change while it is cycling, but that might slow down the process.
You would have to consider the size of the aquarium and the volume of the ice cubes. Too cold too quick would not be good at all.
As far as the running of the tank and the efficiency of the filter is concerned, it doesn't matter if the water splashes down into the tank or flows quietly into it provided you are getting a maximum flow and the filter is cycled.
It would really depend on the length of time that the bone was in the water, and the type of bone. If only dropped for a moment into the water, then any type of dog bone would not likely cause any problems. However, dog treates shaped like a bone, left inside the aquarium for a day or so, would cause the water to fowl, killing the tadpoles. Rawhide or real bones would likely take longer to have any effect, as they don't break down quickly, but long term would also likely be best removed from the aquarium.