Green Water Problems

Green Pea-soup During the second year in our pond our fish had babies, and the adults were growing at an amazing pace. We started with 12 fish, a mix of goldfish, shebunkins, and ghost-koi, all of which were about 3 inches or smaller. Now the ghost-koi look fantastic and the biggest is about 12 inches long and looks very stocky and chunky. I'm sure he'd make a good dinner (only joking). For the first year the water was lovely and clear, even in the summer, and we had good cover to provide shade from the marginals, like lilies, water hyacinth, and "Fairy Moss" - that red-leafed surface cover weed that can take over the pond and you end up scooping out handfuls of the stuff. Also in the boggy area of our stream we had a good variety of bog-plants; Marsh Marigold, Horsetail Rush, Water Musk. The main pond, now covered with netting since we lost 2 beautiful carp to a heron.

But, in the second year (Summer 2004) things suddenly started going wrong. Three things seem to be the culprit:- The fish were much bigger, and eating more, were therefore excreting more. Even though we put more of the Fairy Moss in the pond to get more cover to keep out the sun, it didn't survive, we think the fish were eating it(?). The yellow-flowered Water Musk had pretty much taken over the entire bog-area, and so we had a mad fit and removed ALL of it! Ooops! Within about 2 weeks the water went a pea-green, taken over by fine water-born algae. We couldn't see below about 4 inches, any deeper and the fish could only be made out as dark shapes passing below. In hindsight we now realise that the plants in the bog-area, with their massive root network, were acting as a wonderful natural "veggy-filter" to eat up nitrates in the water, hold back any crap being pumped out of the pond coming back down the stream, and provide a home for bacteria that was helping the whole "balance" process. When we designed our pond, waterfall, stream and bog-area, we didn't really appreciate what a clever design we had given "nature" to work with. And we had just messed up big time by removing the most vital part of the cycle. A natural vegetable biological filter. Initially we didn't figure out why it had happened. At about the same time the fish had been traumatised by the heron eating two of the larger fish, and we thought the water was cloudy because they were stirring up the bottom silt to "hide themselves". I was also starting to get very fed up with cleaning my Bio-Force filter literally every 2 to 3 days, and having to remove the Cascade water pump from the pond every week because that too was getting clogged up, mostly by blanket weed. I knew that sunlight was going to be a major cause of the algal-bloom, but I was starting to get concerned about the state of the water and the health of the fish, the water at times was almost looking "black", and so started my quest to learn more about what was going wrong and how to resolve the problem.