Pennywort grows like a weed, in my stream ponds, sort of grows in the big pond. I don't think there is enough nutrients for it. I have not put any into the pond bog.
Cardinal plant, I had two, in reading up on them they don't like the real wet of the pond bog. I put some in my land bog, carnivorous plant bog, they are doing great now. Marigold, I had, but think the other plants over took it, one year just gone.
The only time I have algae in the bog is early spring, any wet sunny areas get some slimy green stuff, it goes away as the plants grow, no hair algae.
My pond and bog are full full hot sun, south slope. Sunrise to sunset, very little break in the amount of sun hitting it. The apple trees give a tiny amount of shade for a brief period during the day, late day. The maple tree give a tiny bit of shade to the bog as the sun migrates around.
If you want some more penny wort to try again I can send you some.