The Problem With Algae

When I saw what had happened to the pond I was aghast. My aunt was trying some things like putting in barley straw, but that seemed to have made it worse. Sadly, she also put in chemicals which I believe made it worse and better. Let me tell you a little about algae. Algae can be caused by huge amounts of nutrients in the water. These nutrients are made by grass cuttings, leaves, pretty much any decaying plant or animal matter, including feces. Algae is very bad for a pond besides being an eyesore. A little bit is good, for it provides shelter for animals, and some food. But excessive amounts is bad. Firstly it blocks sunlight from reaching plants and animals below so the temperature lowers. It also does not let air touch the water which is the major reason oxygen is in water. Though algae produces oxygen thru photosynthesis it takes oxygen at night. This is called respiration and depletes the water substantially of DO (dissolved oxygen. These two problems kill off the life. Plus, on the bottom of deep parts of the ocean are sludge and fish need special adaptations so that they don't sink in the mud. Is this a problem then for the fish in the pond? Maybe. So I was sure that it was a nutrient problem, but when I tested for nitrates it came out 0! What? Some explanations might be that I got this kit last December from my sister and it might be old. Also I never checked for phosphorous which is a lead cause in algae too. (Never had phosphate test strip). I don't really know.