If you have a pond possibly the most important thing in it is the water. You want your pond to be able to support any pond life that you have. You also want your pond to be clear enough that you can see your pond life for your pond to look attractive.
In the wild ponds generally have a lot of water going into and then out of the pond. Therefore aeration and circulation are addressed naturally. There is often also a larger volume of water so it is less likely that the pond will become full of undesirable sludge, gases and nutrients. The movement of water can also help flush out unwanted decomposing organic matter and help keep that pond balanced. Your garden pond will not generally have a natural water source so you may need to help it along.
You can help maintain the balance in your pond by adding beneficial bacteria with a pond additive. These products help keep your pond’s nutrients balanced by ensuring that you have sufficient beneficial bacteria in your pond. This, in turn, reduces the amount of undesirable waste in your pond and so improves the clarity of your water and also its nutrient content.
You also need to ensure that your pond is sufficiently aerated so these bacteria can thrive. If you add an air pump this will help with aeration and water circulation in your pond. This again is, of course, beneficial to all pond life in your pond including the beneficial bacteria.