Fish Tank's Natural Filter

The plants act like a natural water filter in the fish tank of an aquaponics system. This is something I've read, but as the days go by, I see it in the fish tank. First, the odor started going away until it was gone. Then, the water clarity started increasing, and you can see this in the video below:

Chemically, I still need to test the water's pH to see if this needs stabilization. Locally, I couldn't find testing strips or a test kit. I might need to buy one online and have it shipped internationally.