Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
This is just guesses on my part, but here goes.
Is the material acting as a chelator?
Chelators have an affinity for many elements, not just the ones they list.
The level of attraction varies.
If one element is bound to the chelator but not very tightly, and another element becomes present (ie, when you dose) then the new element might get attached to the chelator and the old one gets knocked off.
This would not be good, since presumably the one that was originally bound up was one you did not want in the tank, and the one you have added is a plant nutrient that you want to have available to the plants.
Here comes the guess:
I think plants can remove many of the minerals from the chelator.
Sort of like a soil with high cationic exchange capacity. When the plant removes something that it needs the chelator is available again to grab something else, perhaps one of the minerals you want it to bind to.
Eventually the chelator will bind to something so strongly that it cannot be undone, or else the chelator gets broken down and is no longer a chelator. So you keep adding more.
Here is another guess:
It might not matter when you dose in relation to when you used the chelator. All the elements are connecting and disconnecting, getting used by plants and so on.
If you do wait, lets say 24 hours, it might give the chelator time to bind to the more strongly attracted things so it is locked up and won't grab the fertilizers.
To confirm this you might read more literature about the material you are using.