| In your situation the algae can be limited if the waterlillies are thriving with leaves covering 70% of the pond surface. Without that sun blockage, need to limit nutrient in the water, have solid biological filtration and regular water changes. Limiting nutrient means not fertilizing the plants and having low fish population (small fish only) which is fed sparingly. Goldfish are better than koi in these circumstances. The filtration should turn over the volume of the pond at least once every two hours. For your approximate 1500 gallon pond, that means 750 gallons per hour ...hourly turnover is better. For water changes, 10% per week is the minimum typically recommended. Personally, I believe 20% per week is minimal.
If you are wanting to raise koi other than as annual fish that die over winter or in the spring, see if your local library has Koi Kichi. (A dozen years old, but still the best.) Read it.
If your goal is a pretty watergarden with some fish, get goldfish and grin & bear the algae bloom for a couple of months each year. Fertilize the soil with tree spikes and you'll get the lillies growing like mad. Enjoy the blooms. The fragrance of tropical lillies can be intoxicating. ...but don't expect koi to thrive.
Whatever your goal, I wish you the best. Nothing like water in the garden to make the world seem at peace. |