It happens every year. The algae arrive. What can you do to prevent it?
For a healthy basis the pond needs to be filled with sufficient plant mass. This applies to ALL ponds. Swimming, koi or fish ponds can also be equipped with sufficient plants. They don’t only look good, they also bind the nutrients. By simply pruning the plants the nutrients are completely removed. If algae appear in any form in large colonies, they simply have too little competition. The biomass of the plants is so small compared to that of the algae, that the nutrient uptake capacity is insufficient. This results in a strong algae growth.
What options do you have? When setting up a pond, experience has shown that it is beneficial to build a bog area of 10-20 cm depth and 1/3 of the size of the entire water surface. This area is used as filter, with the result that the fast growing plants absorb the nutrients. If this is not possible, you can put in similar quantities of marsh plants at the fringe area of the pond instead. In addition water lilies, stem plants and floating plants can be positioned in the deeper zones in plant baskets. However this is often not feasible for swimming and koi ponds, since the plants get in your way while you are swimming or they get eaten and pulled out by the fish. If you neither have a fringe area nor a large bog area you can integrate the plant mass by means of floating plant islands or plant baskets. Even small amounts of phosphate are enough to enable the growth of the algae.
Just one small tip. To prevent algae sustainably you need to check the water stability (pH and KH) regularly too. In addition you can shade your pond with an awning or use JBL AlgoPond sorb for a kind of „sunglasses“ effect.