This is kind of rare project for me that is a having a problem, it was my first wetland system and it was an above ground. The company that built the concrete block tanks did a bad job; tanks didnt hold water. We placed liner in the tanks and solved the leak problem. The main tank that we were aiming to filter is 40L X 7W X 3 1/2 D. I designed a new tank to be built on to the far right side of the picture, the new tank was about 10LX 4 W X 3 ½ D. I placed all the recommend rock sizes around the wetland system and built my own wetland system based on aquascapes wetland, then placed a variety of different plants. The pump is about 7000gph. The owner of the tanks has another system that takes all the water off the roof of the building next to the tanks and refills the tanks. This system worked great for about a month, the water was crystal clear. I get about 8 hours of sun on the tanks but I have a form of small algae floating in the whole tank from top to bottom. Does anyone have an idea on something that can be tried?