First all plankton blooms are not green. Some are brown , some are red and many are green and some have little visible color until they reach a high density. Plankton is there in the water but often in amounts to low to see thus resulting in an infertile low productivity pond with clear water. A pic would help a lot towards sorting this out. For example your cutrine plus application would have killed a lot of plankton and may have resulted in the plankton ooze except that you indicated that it occurs over a much longer time (every am). Here are pics of a plankton bloom succession on one of our ponds (1 early green phase , (2 secondary green/brown phase with more zooplankton and (3 late phase late season brownish zooplankton bloom ongoing as the background color and including what is believed to be a red euglena bloom.