Miniscule white creatures

Hi and thanks in advance.

Have a 5.5 gallon freshwater tank with one three-inch fish and lots of
plants. Sponge filter. The fish is not being overfed (it gets 4
small feedings a day, and eats it all).

The plants are finally starting to take over, reducing the algae
population, but I am noticing tiny, really tiny, creatures in the
water. Some are swimming around, and seem to congregate near the
strongest light. Others seem attached to the back glass, which I do
not clean.

The water is changed 20% a week. The side and front glass are kept
clean. So is the gravel.

Any ideas what I am looking at here? They do not seem to be bothering
the fish, and I assume they are eating the algae. They are so small
that I cannot tell what they actually look like.

Thanks again.