Not sure my opinion means much but I do have a koi pond with a very large pressure filter. I only have to clean it 3 or 4 times a year but when I do it is full of little red worms in all of the sponges. I looked it up once upon a time and if I remember right it is completely harmless. Probably due to all the stuff my daughter and I throw in there. We have an albino channel cat that is 9 years old, 1 lone pumpkinseed sunfish, 1 koi that is also 9 years old, numerous goldfish of all the fancy and not so fancy varieties, 1 turtle, and about 15 tilapia. When we harvest rabbits and quail, we throw the hearts and pieces of lungs in to the turtle and catfish.
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