Purigen's main role is absorbing organics before it turns into Ammonia, Nitrite and Nitrate. Purigen is not the best at absorbing colour bodies or tannin. But it does absorb some of it, activated carbon does a far better job. So it only dampens the pH lowering properties of the peat, but it still removes some of the humic acids and colour.
Trace elements released by peat will not be absorbed by Purigen, as it only targets organic compounds.
This is what one of the Seachem tech support guys said on their forum...
"Using Purigen will not have any impact on the benefits of peat. While Purigen will remove the color bodies, unlike carbon and other chemical filtration medias, it does not remove trace minerals. So, you can use Purigen without loosing the pH buffering ability and the trace elements produced by the peat. However, because it will remove the color bodies, the water would be fairly clear and Purigen would not be the product to use if you were seeking a blackwater look to the tank. "
and
" Purigen is an organic scavenging resin that remove nitrogenous waste at an unbelievable rate. It does not remove any other elements such as metals, trace elements, or nutrients from the water column. It removes nitrogenous waste before it can convert into ammonia, nitrite, and nitrate. It has such great capacity for organics, that it has become known as a "protein skimmer in a bag"! It also does a fantastic job at removing tannins and color bodies from the water. "
Just remember this ...
Purigen is not a long term filtration media. It performs a role. Use it only when you need it to perform it's function, then remove it. Purigen should not be used long term in the tank, and left forgotten in the filter or bag.
This goes for activated carbon, macropore and most chemical filtration media as well.