I started to increase the PO₄ content with Eudrakon P. Already the next day, or even after a few hours, there is no trace of phosphate any more although I added the recommended amount!

• In particular in tanks which were very short of phosphate for a long time, the consumption is in some cases enormous. The plants fill up their reservoirs, but every surface in the aquarium binds PO₄ by absorption (including the filter content, panes and floor) too. This may mean that after a very short time no more PO₄ is measurable.
  Normally after a maximum of 2 - 3 weeks, the reservoirs of the plants are full and all surfaces are saturated. Now the phosphate requirement should decrease to the current consumption of the plants (normally only a fraction of the initial requirement).
• We recommend not adding anything. This is a common misunderstanding.
  The instruction only describes the quantity required to increase the PO₄ content by a certain amount in a certain quantity of water. This is not connected with any information on consumption. This can generally not be predicted and is therefore to be determined for each tank by the owner by recording the quantity added and the difference between the theoretically calculated and actually measured phosphate content over several days. If this difference is divided by the number of days of the observation period, this gives the current daily PO₄ consumption.