Hello to everyone. This is my first post at RF, and this is my first question. My aquarium is 160l, filtered by Eheim 2227 wet/dry canister and Sander AH 500 external skimmer. The last reading of PO4 is 0.5, so I have put JBL PhosEx Ultra as on directions (I have rinse in running water and between filter layers). Few minutes after this, water became sligthly green. All fishes and inverts is looking good. What has happened?