A pond heater is used to keep your pond from freezing solid in the winter. A frozen solid pond is bad for your pool liners, koi, and for some pool structures that may use cement.
A person would need a propane water heater if they lived in an area where heat would be needed. Some people who live out in the country and don't have access to other types of heaters.
If you need a heater core, the one you currently have would be leaking. If the car is over heating or not getting warm enough, think thermostat.
We do not have a need for a space heater so I have not used one in the past. I would not use kerosene but I would use electric if necessary. Dyson has one that is pretty cool looking.
A good root system to hold it in place against the current.
Most people would want the spa hotter, so in that case there is no way to use only one heater.
The conditions necessary for a fish pond would be pretty much anywhere you decided to set one up. You will need to dig a hole, cover with a garbage bag lining, place the pond over the lining and fill with water. You will need to treat the water before adding the fish.
There are several pond deicer options available for someone to purchase. Depending on the size of the pond or water source a person wants the pond deicer for, the size would make a difference.
If all the vegetation in a pond were alive there could be many effects that would it have on animals. One effect is population strangulation.
The word "pond" has one syllable.
This is just a guess but you either need a new water heater or you need to adjust the temperature of the one you have.
You need 10 soft clay to build one. I never did it; but I would guess you first build the room, then select the appropriate hotspot in this room.
The humorous answer is to say "there aren't two lily pads in the pond, only one." The mathematical answer is that identical lily pads would take 29 days to fill the pond (not 15), because after the first day, a single lily pad would be twice its size, or the same size as the set of two would be to start out.