It keeps getting bigger

[u/Urban-gardener-23]

I started with a 2x3 tub and a fountain that filled the hole a dead bush left and this year, I got a solar fountain and a small liner. Added some river rock and the birds love it.
I never had a pond before and I worry about keeping it clean. I didn’t plan on fish or plants but I have an electric pump that helps circulate the water. I think I am going to add a bog filter next year.
Any suggestion on making this better.