I was able to keep the following plants alive with a salinity of 1.004. (Which I would think would be fine if you're talking a FW puffer.)
Java Moss, Corkscrew Vallisneria, Duckweed, Brazilian Waterweed, Java Fern, and Cryptocoryne Wendtii.
I also tried Rotala indica, but it was eaten by my Red Claw Crabs before it had a chance to grow.
Well as I said, plants like java moss and java fern will do well in low salintity. As will water sprite and crpyts. But getting up near 1.010 sg will be really hard on them. That is just teh experience that many brackish people have been through. As for planted puffer tanks, most of those are probably either freshwater puffers or else new tanks where the plants haven;t died off yet. But I wish you good luck in trying to get those pknats to work for you. Trying is often the best way to go. Keep us informed if you have success (and by that I mean over 6 months or so).