New Information:
Today I noticed that many ostracods had migrated towards the bottom of the aquarium. I assume that this is because either plant material or dead organisms have settled at the bottom. This gives me the impression that ostracods are scavengers, and it also provides me with information that will be useful the next time I have to search for them.

I also noticed that all forms of diatoms were growing. Cyanobacteria has also increased in number, and I expect it to keep going up. The image above is of a cyanobacteria, thought to be a young Nostoc (a cyanobacteria) next to a diaton (the yellowish figure). This was identified with the help of Microscopic Fresh Water Life by Planskit.

The image above is a member of the algae group, a Eudorina to be specific. It was hard to identify this organism, as most of the suspected culprits all had flagella of some sort, and this one doesn't. I finally found the right one with the help of the book Algae of the Western Great Lakes Area by G.W. Prescott