So, I had an idea. I know - can you hear the creativity wheels turning in my head? Why not plant a little aquaponic lettuce bed right in the turtle tank? Nothing fancy, just a floating bed that she can nibble on when the lettuce gets big enough to drape over the edge.
It would have to be made of materials that would not only float, but not be something she could bite off, swollow, or hurt herself on. It also needs to be high enough out of the water that she can't use it as a basking platform.
I got a plastic container that came from Costco - lightweight and flimsy, and drilled lots of holes in the bottom to let the water in. I put an empty water bottle (lid on so it would stay afloat) on each of the shorter sides, and rigged it up with some hemp rope. It's not completely done yet. I still need to fill it with lava rock and plant some seeds, but tomorrow when I get it all put together and in the tank, I'll share a photo. I hope it works out, because it would not only take the nutrients away from the algae (which is having a growth spurt due to more goldfish in the tank than usual, creating more nitrates), it would also supply Minnow (the turtle) with fresh food.