I put three in my 1/10th acre trout pond because I found literature from Canada that shows they can control vegetation in a trout pond if you up the quantity to compensate for the cold temps. I was able to net one and move it to another pond when I believed they weren't doing much. I still don't believe they are dong much in the trout pond unless they are feeding below sight level however they must be eating some vegetation as they aren't interested in pellets I have thrown to them. Some growth but not a lot probably due to the cold water. Very spooky fish!
I will be adding some to my bass growout pond next spring that is going nuts with chara if I find a reliable supplier. I had one promise to bring me some this summer but he never showed up. I'll have to have Bill Cody the expert to advise me on how many. If I can get him out here to see the amount of vegetation.
If I could get my algae bloom back in the bass pond by reducing the chara I would be one happy camper! I was thinking of adding adult Talapia to reduce the filamentous algae too. Maybe get all the nutrients converted to phytoplankton?