Unfortunately algae which is generally blanket weed will grow at certain times of the year in a koi pond.There are many so called solutions but none of them seem to work in the long term.
You do not say how long it is, A well established pond will usually have about half an inch growth on all the sides and this is considered normal.
If it does get long then you will need to look into ways of removing it. Long strands can be removed using a bamboo split one end.
Most people in this area have their ponds fibreglassed in British racing green. It does not matter too much as the sides will be covered in some type of growth anyway and generally it is green unless it is dying off. I think the part above the waterline which will not be affected looks better in green. Black above the water surface tends to grow greyish in time, and easily stained by deposits in the tap water.
Posted on Mar 13, 2007, 7:37 AM from IP address 81.129.88.105