Hi Samantha, welcome to the forum
Interesting setup and brownie points for re-purposing lab glassware
. I can think of a few things that might help.
1. First the algae in the fish tank is probably robbing some of the nutrients your plants would like so I'd shade the fish on the side toward the window. Doing this will also help the fish with the oxygen levels because algae takes in oxygen at night.
2. If you're using flake goldfish food it might not be able to provide the nutrients you plants need because most of these are for maintenance and not so much for growth like commercial fish chows. Having said this, 3 goldfish probably provide more waste than the filtration you have can handle. That window ledge looks ready for a planter
3. The light levels up high are probably not good enough to support much plant growth without adding some supplemental light. I'd either lower the setup and move it toward the window or setup some other lighting. You could also focus on plants that don't need as much light like lettuce but I think it's probably a stretch without some position adjustments.
Cheers
