Purigen and it's interaction with peat/active substrates

[dao]

So I googled about purigen and it's interaction with peat and this puzzled me.

 

Seachem claims that purigen will absorb tannins, fulvic and humic acids but will not handicap peat's ability to lower the pH... Aren't these acids exactly why peat or active substrates in our tanks have the ability to buffer the pH down? If not then what else is there in peat that allow for ph to drop? 

 

[dao]

To anyone that would also be interested about this, below is the Seachem's answer to this issue:

 

Thank you for your email. Basically, humic acid is released from Peat after it removes minerals from the water, softening the water. This softening effect is unavoidable. Once the Humic Acid is in the water, it promptly starts donating hydrogens to the water, lowering the KH and pH. If Purigen gets its hands on the Humic Acid molecule, it will remove it from the water, but by then the humic acid has already successfully brought the pH down. If you somehow managed to completely surround the peat with Purigen so that any and all humic acid that is released was immediately adsorbed, then yes, the Purigen will have managed to completely prevent the Peat from having any effect on the pH at all. However, in almost any other situation, there will still be an impact on the pH of the system despite the fact that the Purigen eventually removes the humic acid from the water.

Thank you,

Seachem Support

[zodduska]

Hey dao I ran into this question myself recently, last weekend I decided to rescape and restock a long running tank with very old Aquasoil in it (2013)

 

I use reconstituted RO water with a tds of 25 and adding in Salty Shrimp GH+, I had originally been using Salty Shrimp GH+KH to do this for OEBT of long past.. so anyway there is still a bit or remaining KH in the tank.  GH 6 KH 1-2. 

 

PH was in the high 6 range, with PRL incoming I wanted it lower so I added a bunch of alder cones, a large indian almond leaf and a new piece of cholla wood, the next day there were plenty of tannins in the water and PH went down a little to the mid 6 range.

 

Added new Purigen to a HOB filter because I've always used it with shrimp, the next day the water was clear and I decided to check the PH...  7.4!  I was pretty surprised and figured it had to be the Purigen absorbing the tannic acid, googled it like you and read the same responses from Seachem support.  I thought how could it remove the acid yet still leave a low PH?  Seems contradictory.

 

Removed the Purigen, changed water, PH is now back down below 7.

 

The Purigen's effect on my water was more pronounced than usual because my substrate's buffering ability has likely significantly diminished over time compared to my initial experience with using Purigen in the tank, a new substrate probably has much more ability to counteract the absorption effect.  I've also changed over 100% of the water in the last week so hopefully over time there is still enough left in the Aquasoil to keep the PH low.

 

YMMV.