Rice in caldero is cooked in a soup pot and is soupy. When making paella or any other Spanish rice dish, don't wash the rice, for it needs its outer coating of starch. Then turn down the heat. Cook paella and other rice dishes uncovered. Unlike risotto, they are not stirred after the first bubbling stage.
Some cooks like to shake the pan briskly to keep the rice from sticking on the bottom.
Others love that crusty bottom. The rice cooks in 18-20 minutes. Remove the pan from the heat when the kernel is just cooked through. Sometimes you will need to add additional liquid. Any rice dish, whether dry or juicy, needs to rest off the fire at least five minutes to finish cooking and absorb liquid.