So my 3 week old WC system seems to have algae in the reservoir. Some foam with green stuff has developed on the top of the water level and when i tried to pick it up with a tower, the color was green. I have attached a picture: It is not easy to see the green as this is a phone camera with flash. I am using Mayhems pure H20 with anticorrosive liquid and mayhems biocide. Three weeks ago I put 1 drop (for 1 litre of fluid currently in my loop) and last week i put another one seeing this foam. Now I tried the PH indicators that are provided with the biocide bottle. When I put it inside the foam, the colour is dark green (around 8+ PH but when I put it on the other side of the reservoir the PH is about 7). Today I put 4 drops and 10 minutes later there is only half of the foam. The foam seems to "prefer" the reservoir walls, as it is always stuck on the plexi and never tries to float away. Note: I DO USE THE COVER ON TOP OF THE RES!!! just removed it for the pic! Can you please help me determine my problem? Here is a pic of my system 3 weeks ago: Tonight I am leaving home for three weeks. Should I leave the WC loop as is or empty it due to this algae issue? Thank you for any answers. Sorry for the huge pics, not used to uploading pics on 3rd party sites. I have also posted this thread on overclockers.co.uk forums.