Your fish will be at their most active in the summer months as the water temperature is higher. As temperatures rise make sure your fish are getting sufficient oxygen, if oxygen is lacking you will notice the fish gathering near water flow areas or gasping at the surface as this is where oxygen levels are at their highest. Increase oxygen levels by encouraging water flow at the surface of the pond with fountains, waterfalls or moving filter outlets to above the surface.
Additionally, consider introducing an air pump and air stone to the environment to provide extra surface agitation – this is particularly important on those hot close thundery days.
Summer is the best time to introduce new fish as your biological filtration is matured – however do not overstock your pond as this will increase the chance of fish health problems (see how many fish can I have in my pond?). Introducing now will also give the fish time to gain strength and adjust to a new outdoor environment before the winter.
Continue to feed plants regularly to encourage healthy plant growth. Cut back dead leaves to stop them contaminating the water. Encouraging plant growth will also increase surface cover which will prevent blooms of algae like Blanket Weed and green water algae. Add floating plants like water hyacinth, water soldiers, water chestnut and water lettuce to increase shading and rapidly remove excess nutrients (and they’re pretty).
Regularly maintain your filters and pumps monthly or as the flow reduces indicating maintenance is required, cleaning/replacing foams and removing blockages to keep water clarity and a healthy environment.