Yes i did. I use Salifert. Lets say it was test error but the amount of time it took to return to normal kh levels by upping the dosage with a about 5mls daily on my 250L system the math plays out to about 0.6dkh drop extra that particular day. Maybe it was due to the GFO and calcification of corals because of po4 drop.0.8 dKh is a large drop. Did you test more than once? What alk test were you using?