With the video I understand. What you have is very normal.
Thousands of algae species. They come and go, most ponds will have several species at the same time. Different species complete with each other including chemical warfare. As things change different species can gain an advantage and kill another species.
Most algae species cannot survive for very long in a pond, say a few months. There's always another species waiting to take advantage of whatever state a pond is in. In new ponds this cycle can be sped up because the pond changes state a lot, so each species of algae comes and goes faster.
The state you have in the video is the result of one or more species of macro algae having died off. It can appear alive, and to some degree it is, just like any plant, death is more relative than it is for animals.
You can vacuum out the dead stuff as much as you like. This can be as complex as emptying the pond and shop vac out everything and scrubbing, chemicals, as far as you want to go. Or you can keep the water in the pond and use
another type of vacuum. Or you can just
use a net to scoop out a lot of the dead stuff. Or you can go to the other extreme and leave the muck to have a Wildlife Pond which is whatever nature decides to give you. Point is there is no right or wrong way, just whatever way you prefer.
Except for using chemicals there is no way to prevent future algae any more than there's a way to stop weed from sprouting in a garden. Like weed seeds algae is everywhere only more so.
There are however endless wild ideas on how algae can be stopped. From magnets to anything with the word "
barley". All of these have one thing in common, 6-8 weeks for them to work. Pretty good bet any species of algae will decline in that period. It's like a cure for the common cold that takes 10-14 days to work.
Most of the "cures" out there are pretty harmless and not too expensive so no great harm. But if you really want to get serious about algae control it's really pretty simple, but work. No different than a garden or lawn. When macro algae is growing you pull it out.
Whoever told you doing this released spores so you'd get more algae is an idiot of such monumental proportions that other idiots would be embarrassed. Algae can reproduce just fine all by itself thank you very much. Pretty sure they don't rely on humans to reproduce. While it is true broken bits of algae can root and grow it makes zero difference since the algae is going to fill the pond on its own.
When pulling algae is done you will see a problem with potted plants in the pond. It's a pain when the algae is all wrapped around the plants. My solution was to place plants in their own beds around the edge of the pond or even out in the pond. Keep the water these beds below the "soil" surface so there is no standing water and therefore no algae in the plants. Makes pulling algae way easier.
All marginal type plants also do much better when not submerged. Many plants are sold saying something like 6-12" deep. That's the maximum depth which many people take to mean the required depth. Water lily has to be submerged, and there are floaters and some plants have to be fully submerged. But marginals...above the water is better.
The more you can dismiss crappy info the easier it all gets. Otherwise the "cures" are endless. More are made up everyday.
