It might be a good idea to check the water level of your pond. Make sure there are no leaks.
There is no need to break the ice on the top of ponds, there is still enough oxygen for the fish in the water.
Use nets to cover up ponds, this will prevent leaves and other things from polluting the water.
Ponds should be netted sometime this month, falling leafs can be a real bother.
Ponds and water features should be kept topped up at all times.
When you spot yellow coloured water plants you should remove them asap. If they rot it will decrease water quality.
Remember to switch from spring fish food to summer fish food as i contains a higher amount of protein.
The right plant balance is beneficial for the water, if the pond is in full sun, 50-70% should be covered with plants.
Remove any algae or blanket weeds from your pond and remember to keep it topped up.