During this high summer month plants will grow optimally and water lilies are in full bloom. Regularly cut finished water lilies away. This will be for the benefit of flowering. Also prune other pond plants and keep some open water. You can put these plants next to the pond for a while so insects can find their way back to the pond.
Owing to luxuriant growth especially of oxygen producing plants, lack of oxygen may arise easily during the morning hours. The reason is that at night no oxygen is produced, whereas the plants do absorb oxygen. In that case an air pump will be the solution.
During this month the temperature of the pond water may rise too as much as 20 °C. Warmer water will contain less oxygen. Moving water by means of a pond pump or an air pump can prevent any lack of oxygen. Owing to higher water temperatures fish will have more need for feed now. You may therefore feed your fish liberally. Administer every now and then a few rain worms and some pre-soaked lettuce. The fish like that.
During this period water lilies are endangered by the so-called lily beetle. The larvae of these beetles attack the inner side of the leaves, which results in their turning brown dying quickly. The only solution is to cut off and remove any leaves attacked regularly, using special equipment, for example the Pond cutter & Pond pincers. The sooner you do this in a logical way, the less you will suffer inconvenience.