Not sure why my response did come through the 1st time, I'll post another.
The Fe in the substrate might be such that it binds with PO4 intitally, after a few months or by the time all the active sites are filled with PO4 other anions, the tank will ease in to a more plant domianted PO4 removal rate.
Fe is added for PO4 removal in lakes, some makers might believe this is a good thing to remove from the water column and sequester in the substrate. Then plants can remove it via the roots or reduction, although this takes a lot more reductive power than is typically present in aquarium substrates except soil and peat based substrates with high OM content.
Laterite does a similar thing with PO4. But there is only a finite amount of PO4 that can be bound. As your tank/substrate ages, there should be a decline.
There's no way 2ppm is used this fast.
The 0.1ppm fraction is either test kit error(test against a known standard rather than against another cheap test kit), or Orangic PO4 that is not used by plants. Often there is a fraction around 0.1-0.2ppm that is never removed in tanks and plants cannot remove it.
Regards,
Tom Barr
The Fe in the substrate might be such that it binds with PO4 intitally, after a few months or by the time all the active sites are filled with PO4 other anions, the tank will ease in to a more plant domianted PO4 removal rate.
Fe is added for PO4 removal in lakes, some makers might believe this is a good thing to remove from the water column and sequester in the substrate. Then plants can remove it via the roots or reduction, although this takes a lot more reductive power than is typically present in aquarium substrates except soil and peat based substrates with high OM content.
Laterite does a similar thing with PO4. But there is only a finite amount of PO4 that can be bound. As your tank/substrate ages, there should be a decline.
There's no way 2ppm is used this fast.
The 0.1ppm fraction is either test kit error(test against a known standard rather than against another cheap test kit), or Orangic PO4 that is not used by plants. Often there is a fraction around 0.1-0.2ppm that is never removed in tanks and plants cannot remove it.
Regards,
Tom Barr
