Agree with Paul about the cover, which will cut down the algae but not eliminate it. Most algae eating fish are not tolerant of cool water. My experience with snails is that they don't eat enough and obstruct the pipes.
Also 25 channel cat for 150 gallons is not going to be sustainable.
Unless your water has turned pea soup green you have nothing to worry about. Any healthy system will have dark green algae on the sides of the tank. So do lakes and streams. You have not really described a problem so far. Do not expect a "clean room" look to your system or you will kill it. A certain amount of algae indicates a healthy system.
If it is on the web it is here on this forum. Algae control is not rocket science. Andrew already has a handle on this.