Did Anybody Here

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Order Pea Soup??
By Bob Heagey

Ah, the sights, sounds, and smells of spring and early summer around the pond. The fish are frisky and very hungry, eating as much food as 3% of their weight among five feedings a day. It seems they are spawning every few days. You do a water change to get rid of that excess ammonia and they spawn again. The lilies and bog plants are just beginning to grow after their dormancy so you feed them with the proper fertilizer to get the most out of the early spring growth. The toads and frogs make a heck of a racket into the night laying their strings and mats of black pearls. The fish gobble up the mats but leave the strings to develop into tadpoles that feast on hair algae or your favorite plants. Life is everywhere. And then there's 'Soup du jour', usually Pea, rarely Bullion. Why does this happen when things are going so well. Especially right after you added that special brightly colored koi with a name you can't say, spell, or even remember. Well, lucky for you 'Soup de Jour' is just that 'the soup of the day', or week, month, season. It actually isn't so bad, unnatural, expensive, or even hard to eliminate. A look at the nature of the beast will yield both secrets and questions.

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Bob explaining things at
a recent pond installation.

Hutchinson introduced the "Paradox of the Plankton" as how so many different species of unicellular algae or can thrive without one becoming dominant to the exclusion of the others. One explanation is that of "contemporaneous disequilibrium", that is, the cells are floating around in such random haphazard manner that they are never in one place long enough to make a difference.

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One of Bob's Best Koi

Does anybody ever order pea soup on purpose?

In laboratories and fish hatcheries there are scientists and aquarists that go to great lengths to produce pure cultures of select species of algae. These algae are critical for the culture of zooplankton which is typical first foods for larval fish. Algae producers constantly toe the line of the carrying capacity for algae culture. Population crashes and contamination by another species are common as algae can double their population in as little as a few hours. With that fast a doubling rate the algae culture can starve if and when the nutrient food supply is exhausted.

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"Bob Heagey bred Koi"

Back in your pond that culture, or pea soup, is balanced on the brink. It gobbles up nitrates then dies and recycles nutrients within your pond. A close look at your water clarity will show a surprising clearness late at night as opposed to late afternoon. The beast can even swing your pH and oxygen levels to really stress your fish. During the day the algae are converting CO2 to O2 driving the oxygen levels to maximum. The lack of CO2 and accompanying carbonic acid (H2CO3) drive the pH up to dangerous levels where ammonia becomes un-ionized and very toxic to fish. At night the algae, being a green plant, respire to consume O2 and produce CO2. Low oxygen and high CO2 makes more carbonic acid which drives the pH down. A couple of cloudy overcast days in a row can spell disaster for large earthen fish ponds under bloom conditions as the lack of sunlight will cause a massive die-off of the algae so that oxygen is no longer being produced and the decomposition of the dead algae further consume critical dissolved oxygen to severely stress or even kill the fish unless supplemental aeration is provided. This sounds really bad but your pond is hopefully buffered to stabilize the pH and the constant aeration from your waterfall or filter return will keep the gases in check.

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Bob's Fry

The beast is feeding on all those nitrates that built up over the winter when the water temperature was too cold for algae to grow. Once the water temperature reaches the minimum the algae growth then boom you have what is called "bloom conditions. As long as these conditions are good for algae the soup stays thick and green. Water changes may help, but some municipalities have chloramines in the water which will feed the beast. You could let it run its course, but it could continue through summer if there are no plants to consume the nutrients. Now, how can you be fertilizing the plants (and algae) while expecting the plants to out compete the algae for nutrients? Simply put, shade is the key here. The lilies will eventually hit that magic 70% surface coverage and the algae will be starved for light. In the absence of lilies you could provide a shading structure over the pond. There are even dye additives that will accomplish this. I'd stay away from chemical treatments that kill the algae as that would only load the system with dead decaying organic material and start the process all over again. I like to simply strain the algae from the water by placing a basket of polyester floss at the base of the waterfall or return. Simply wring it out or discard it when clogged and full of green ooze. Another popular treatment is the Ultraviolet (UV) sterilizer which zaps the cells as they pass through a tube of ultraviolet light. The UV also kills bacteria (good and bad so install it after your bio-filter) and other unicellular pathogens. The trick here is to mechanically remove the algae faster than it is reproducing (remember that doubling rate). Oh yeah, if your raising fry indoors and want green water to feed them, good luck; it's near impossible to get good green algae blooms in the low level light and sterile clean culture water conditions of indoor cultures.