It is certainly true that fertilization is not for every pond, and the problem can be too much or too little water.

If your pond has too much water running through it, it cannot retain the fertilizer, and you will never get the bloom you want.

If your water volume drops too low during the summer due to evaporation, then the concentration of fertilizer and the amount of planktonic life may increase to levels which result in oxygen depletion. This is because phosphorus, the main ingredient in good pond fertilizers, doesn't gas off like nitrogen. What you put in stays in unless and until it is washed out.

Having said this, I have fertilized my pond every year, and it has paid off in large numbers of fat bluegill (my favorite fish) and good-sized bass (my friends' favorite fish.)

I should add that I do not see the sense of fertilizing in February or March. I have never had a bloom that early, and in my area only the filamentous algae are fed that early. I now first fertilize on tax day, and that schedule works very well for my pond.

I have learned to take into account how far the pond will drop in very dry years. I leave my bloom a little on the light side until I have a good idea how much net water volume loss I will have for the summer, adding more fertilizer if necessary once I know it is safe. So far, no fish kills.

So, if you are willing to bear the expense of ultrafine granular pond fertilizer and are willing to be patient in adding your fertilizer as directed, I would encourage you to seriously consider whether your pond and personality are right for fertilizing and to act accordingly. (You also must take into account that most of the female set will be grossed-out by a good bloom. "Sanitary lagoon" is the kindest thing my dear wife has had to say.)

I have been told that research in northern ponds showed no benefit from fertilization, but I don't know for sure if that is true, and in southern waters, research has shown just the opposite.
Lou, 13.5 acres

When roses are red,
My pond is green,
And when it blooms,
It's a big fish machine! ;\)