Of the forty fertile ponds, we also fed five varieties and sizes of Silver Cup pelleted fish food. Protein and pellet size was determined by species and sizes of those fish. Protein ranged from 32-48%. Tiny fish and top line predators got the high protein, intermediate forage fish such as bluegill get the lesser protein.
I have not considered using dye and fertilization in combination because I have seen them as conflicting. I have also thought each renders the other moot. Finally, I have tended to look at each of those serving two completely different purposes. So, you have brought an interesting consideration. I have put dye in small lakes and ponds in late winter, hoping they could help put off rooted plant growth long enough for us to get a bloom. These ponds are typically ones we aren't able to attend to as often as we probably should. Sometimes it works quite nicely, sometimes it doesn't. I have learned each pond has its own 'personality' and once we figure out what works, we tend to stick with it.
In urban settings, we use dye simply because these landowners are less interested in fish production than having their pond aesthetically appealing. We don't particularly care if there are plankton or not. We mainly want no rooted aquatic plants, and a pleasant color for the owner.
Your last question...we try to maintain a secchi disc visibility depth between 18-24 inches for the safest fish production. Plus, we have learned to 'read the bloom.' That's important, too. When fertilizer is properly used, when water temperatures are consistently above 60 degrees in spring, we get a bloom within 5-7 days. The water turns a vivid green, almost the color of split pea soup. That's phytoplankton. Then, water color shifts over the next few weeks. It changes from vivid green to an olive color, then an olive/brown, the brownish/olive, then brown. As zooplankton feed on phytoplankton..that's why the water color changes. As the color shifts toward brown, we often nudge the bloom with a small dose of fertilizer.
Measuring the plankton tends to show it migrating in the water column, dependent mostly on sunlight. During dark hours, plankton may drop close to the thermocline, then rise to the surface during the day. So, the best answer I can give you for the last question is that dense, shallow blooms are usually the ones which scare me the most. A dense bloom, with visibility less than 10 inches, is scary. The thickness of that bloom may only be 10 inches, but it may be 30 inches, too. That tells the tale how scary it is. Thick blooms with shallow visibility are candidates for oxygen depletions, especially if the water is green.
Here's my parting thought about fertilizing and plankton. I see this as a temporary resource to serve specific purposes. If you want maximum production of baby fish, consider fertilizing. If you want to get a head start against rooted macrophytes, consider fertilizing. Many fish culturists feel compelled to fertilize during the entire growing season. I don't necessarily believe that. I think you can fertilize in the spring, feed babies, get ahead of plants, then let the bloom go through its cycles and not feed it again. Water clears, baby fish feed predators, rooted plants are put off long enough they likely won't become as serious a problem. This is my style of management.
