OK, my sword plant is ported in a 4" herb pot for now, Acrorus is in a
6" pot near the top.

Now my question about the filter. I asked about adding an aquarium
filter, but my fountain pump already has a big sponge cylinder over the
intake. 600 GPH per hour, this is already providing pretty good
filtration, right? I can just take it out and wash the sponge
regularly?

Would the goldfish die from the heat? I checked temperature it gets
to over 80 around 5pm. 1pm-5pm would probably be the worse times.
The fountain is on a bubbler nozzle I don't think there will be a lack
of oxygen.

I was under the impression the goldfish will eat anything when they are
hungry enough, like the Anacharis and other plants to support
themselves.