I think they are saying they use Purigen now and want to know if the pothos will be hurt if they add pothos to the tank. The short answer is no, the pothos is tough enough that it'll be fine - but it may not do as well as it would if the Purigen wasn't in the tank. Here's where it gets tricky, if you are running Purigen now adn still seeing any nitrates, there's a 'food source' for the pothos - but the plant will only be able to use a certain amount of 'food' too. If the plant is small, and the nitrate is small, you may add the pothos, the pothos uses the nitrate available and you notice the nitrate level drops off. The plant will grow to fit its food limits too. So, if you start with a small amount of nitrate and a large pothos, you'll still see the nitrate drop off, but the plant may not grow and may even yellow or drop some leaves if it's not fed enough.
This is extreme though - my mom kept the same pothos in a glass jar for years, giving it city water once a week. I'm sure that poor plant was starved to some degree, it never grow much over all those years, but it didn't die off either. It was limited by the amount of 'food' it could process out of the water.
Pothos also likes the sun. I moved a tank from the bedroom to the living room this past year. In the bedroom the pothos had the short end of the tank to hang over, blocking the sun from the west window from streaming into the tank too much. The pothos loved it. It put out leaves like crazy. I moved it, the same setup, into my livingroom. The pothos not had a north window a foot in front of the tank for light. Over a few months the pothos died off on me. It was simply not enough light, and I didn't want to add more light in this room either. I may try some pothos in my sump under the tank with a light source though.
If you want to give it a try, go for it, pothos is tough, just give it a little food an light and start small.
