I recently had a fish die-off due to a disease that I couldn't identify. I need to break down the system and clean everything. Can I use my plants or do I have to throw them away? Is there a way to ensure that they are disease free?
If you cannot identify the problem, who knows what you can do to ensure they are safe.
You can bleach or potassium permanganate dip the plants; grow them in a fauna-free environment;grow them emersed. Randomly treat them with chemicals.
Personally, plants are pretty cheap, far cheaper than risking future luvestock,... So I'm with Fishorama above, just ditch them and get more and grow those.. it can be incredibly cheap if there's a fish or plant club locally to you . You don't say where you are.
If it's something incredibly rare, I would split depending on the plant, grow some emersed, dip some in different chemicals and grow separate without fish .
Personally, for me, the effort needed to keep the plants is going to be far more than the health of new fish is going to be worth.
dougall went into much it better than I did, but without knowing what disease you might be dealing with, just get rid of all plants.
What signs did your fish exhibit? There only a few diseases that scare the bee-jeesus out of me...but they do!! Mycobacteriosus (sp? fish TB) is the major 1...& I've had it only once or twice, ever...even suspected, it's not something to ignore even a possibility of infection. Other than that everything pales in comparison, not that that aren't other bad diseases, but most are treatable if caught in time...
Both dougall & I belong to plant/fish clubs & have several tanks so we're less affected by plant losses...but be careful!! It's not worth a few plants.
If the OP is referring to plants purchased a chain pet store, those plants are typically much more expensive than the fish sold at that store. If so and you want another tank, setup another tank for those plants. Setup another for new fish and plants.