A new algae bloom is bright green. The more water you look through the more green you would see. So your first sign will be looking through 15' to the bottom. If you really want to test you can make a Secchi disc.

Non green cloudiness would be something other than algae. There are non green algae, but pretty rare in pond. The cloudiness can be many things including suspended clay, bacteria, and even reactions with minerals from the source water.

wow, please post a picture of that pond, I want my second pond that big. I have one question, I've been dreaming up this pond for a year or so now. First, is the pond rock bottomed? Also, just wondering if you did what I dreamed up. If your pond is deep (4 + feet), do you have underwater current going to a drain? I'm not a koi breeder, but I love growing big koi, information I've found is that fish are healthier in a stronger current.

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