Update on my aquarium:
My high school has the luxury of having something called the "Student Wellness Center", a room where we could hang out during break and lunch before everything shut down. There was a fish tank of guppies there along with some plant-only aquariums, which were moved out when the school closed. I contacted one of the teachers about these fish tanks and she was happy to let me pick up a few guppies and this sad thing (it was one of the plant-only aquariums but all the plants died):
I separated the large rocks, gravel, and soil, and scrubbed out the insides:
I then tried filling it with water, but I didn't use something that would disperse the flow from the faucet so it turned out dirty on the first attempt. Using a paper plate solved the problem:
I added one of the massively overgrown Aponogeton plants from my other tank and some water conditioner/nitrate reducer. I plan on using this to house very pregnant guppies and their fry, since they produce relatively little nitrates and the rapid growth of the plant means it can almost certainly maintain nitrate levels:
Here's my 10-gallon aquarium with the guppies added. The teacher also gave me some rocks and glass beads, which I used to decorate the tank a little:
Here's a closeup of the new decor with some of the guppies. I can definitely tell which fish are males and females, but I'm not completely sure on how much bulge means a pregnant female:
So far, the fish are schooling, healthy, and eating well. If you have any suggestions on how to improve the aquarium, please let me know.