Pond Boss Forums MANAGING AN EXISTING POND Fertilization phytoplankton, zooplankton is there a TEST?

If you have visibility of 24" then you do not need to add any fertilizer. The danger to adding more fertilizer with that amount of clarity is that you can very easily over-do it and have too big (dense) of a phytoplankton bloom, which will create a fish kill at night if you don't have an aeration system in place.

Adding fertilizer will turn a brown bloom green, but at the same time if you add too much then the green can get too dense. If you start feeding the fish that will help you in two ways. 1) it will feed the fish directly. 2) the excess nutrients that pass through the fish will feed the phytoplankton in the pond which will increase the fertilizer in the water, feeding the "bloom". The "bloom" only feeds the smaller fish (swim up fry and fingerlings) while the feed (depending on the size of the pellets) can feed fish from fingerling size to adult size.

If too much fertilizer (i.e. nutrients) is added via "fertilizer" or indirectly via fish food, you will have too dense of a bloom and the only way to mitigate (remove or lock up and make unusable) is to do a nutrient abatement procedure via Alum or another product that ties up "P".