Pond Boss Forums MANAGING AN EXISTING POND Fertilization fertilizing an existing pond

I share your concern, and I also agree that your water is carrying too much bloom when the secchi falls below 18". Inorganic fertilization is practically immediately available and can quickly ramp up to more bloom than desired. Once there, it will take time to dissipate as the nutrients are recycled as organisms eat the phytoplankton and discharge wastes. As those organisms are consumed, then the fish recycle nutrients in their waste. So it ramps up faster than it ramps downs.

I see you are feeding. Feeding rates in excess of 5 lbs/acre-day will also sustain heavy blooms and there is absolutely no reason to fertilize, if you are feeding fish at per acre rates like that.

There is one thing I would like to mention. Metabolism is driven by temperature. Even phytoplankton have metabolism and they reproduce and grow slower in cooler water. In terms of your native nutrients that remobilize each year in a cycle. Temperature plays a big role there to. The warmer the water gets, the more organisms responsible for nutrient cycling return nutrients to the water column. In the cooler months, the slowing of this activity will cause a corresponding decline in bloom. This isn't a problem ... at least in my way of thinking. In cooler water, the fish need less consumption and do in fact consume less. Its a cycle where water should be clearer in winter and ramp its bloom as temperatures and metabolic activity increases for all of the pond's life (whether phytoplankton, zooplankton, insects or fish). This is a natural annual cycle.

Your biologist is making a judgment if February or March that is influenced by a cycle that is only beginning to ramp up at that time. Maybe, don't bring him out next year in March. Maybe, bring him out in May or June and see if he says to cut back on fertilizer?

One last thing. Sechi depth is not the only measure of productivity. Sometimes water is more productive than the secchi depth would otherwise suggest. Common reasons for this are vibrant periphyton communities and/or abundance of phytoplankton grazers.