A pH of 6.5 to 8.2 is optimal for most organisms. Rapidly growing algae or submerged aquatic vegetation remove CO2 from the water during photosynthesis, significantly increasing pH levels. pH levels > 9.0 begin to be harmful salmonids (trout) and perch. Rainwater naturally has a pH of 5.5; pH < 5.5 is harmful to freshwater shrimps, snails, and clams; metals normally trapped in sediments may be released into the acidified water.

                          Acidic < 6.5 pH       Basic > 7.5 pH .
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