The dead algae is decaying and using up more of the oxygen in the pond. The koi
may be feeling the stress of the reduced oxygen.
Algae fighting tips
~ New ponds and spring ponds need time for plants to get established, algae is
quicker at getting going!
~ add plants, of any kind, in the pond. Especially underwater plants.
~ Shade is good - provided by lily pads, floating plants or artificial shade
for part of the day.
~ LOW fish stocking (20 gallons per goldfish, 100 per koi) and *not*
overfeeding the fish.
~ building a mechanical filter to screen gunk.
~ build a veggie filter, run water through plants, as easy as floating water
hyacinth in your filter.
~ clean up dead plant matter and screen for falling leaves
in the fall.
~ water movement, occasional water changes of 10%
~ add a sludge consumer, concentrated bacteria.
I use <A HREF="http://united-tech.com">http://united-tech.com</A>
~ building ponds with bottom drains and skimmers.
~ do not use algaecides, they only make lots of suddenly dead algae
and that will feed the next algae bloom.
~ do not worry about algae that grows on things (substrate algae) this is good
for a pond
~ gently remove string algae
~ patience and time ;-)
k30a
and the watergardening labradors
http://www.geocities.com/watergardeninglabradors/index.html