I've printed the following modifications and tools for my aquarium with success.
Duckweed Scoop w/ brace bars-- note: The tinges are close together. When I added a brim, it fused the first few layers and made it annoying to clean up.
Link: https://www.thingiverse.com/thing:4232833
Filter Media holder-- I printed on its side. It needed some support, and removing the ones on the top next to the handlebar took a minute.
Link: https://www.thingiverse.com/thing:4564297
I printed 2 kinds of water flow baffles.
#1 https://www.thingiverse.com/thing:5214131
#2 https://www.thingiverse.com/thing:1994922
The first one is a spray bar with an open end that you attach a separate end cap. This one worked well, but when I think it's going to be too hard to try and shellac the deep inside with the acrylic spray. The second baffle is much shorter and open. It's very easy to spray the inside. The only problem with baffle #2 is the inlet tube is small enough that the water pressure pushes it out. I am thinking of super-gluing a rubber band to close the gap and create friction.