Hi again,
I dose into my sump, and after there it goes to my huge skimmer (contains 250 LITER of water, before it goes back to my tank.
I think that because my skimmer is that huge and effective, I dont have(or not see) any leftovers coming back to my tank - but I rarely need measure Po4, and tank is very healty.
Please remember that this is my dosing after long time of finetuning - if u dose too much, u will be to low on phospate - and the corals will become pale and eventually die.
Once every month i vacum my sump, there i can see particles from the seaklear.
Hope it helps:beer: