Thanks! I’ve been looking on YouTube for some how-to’s.
In the spring, try to locate ‘floating water hyacinths’ - usually #2-$4 each, and get 30 or 40. Throw them around the pond, and their roots provide food for Koi. The hyacinths put up a blue flower spike and also multiply rapidly, so you can snap-off the ‘babies’ and they’ll grow into ‘mamas’ and repeat the process.
They cover the surface, hiding the Koi from predators, suck-up algae thru the hairy root system and bloom from the nutrients.
DON’T get water lettuce; they’re prone to aphids and worms, turn yellow and look like crap after the Koi eat their roots.
Covering 40-50% of the pond’s surface with shade plants - 1-2 potted waterlillies, potted lotus, water hyacinths also keeps green algae production way down when the warm spring weather arrives. Those plants’ roots uptake the algae and use it as nutrients.
All the fish shit and uneaten food (bottom of pond should be cleaned-out in early spring) begin to convert nitrates to nitrites, or nitrogen, which feed algae and will cause an exponential growth explosion, turning your pond into *split pea soup* and you won’t see any fish. This’ll happen very quickly when hot weather arrives, unless your pond is balanced.
Chemicals are one way to fight it, but remember that chemicals act directly on fish and cause cancer spots and stress, two bigger killers of sensitive koi. A handful of *water softener salt* will help soothe the fish and provide nutrients back to fish. Try to avoid chemicals; be a “pong manager” and see ahead which problems are coming, and act to head them off. “Balance” is important.