That bottle of black stuff looks about the same as what came out of mine. Carbon as far as I could tell. Not so with the primary filter. Shortly after I purchased my cars I did the purge thing. Now I know what goes in the tank, so don't know if I'll do it again. Someone with a can lying about, may post ingredient list. It's very long. chomamma....I agree, not algae, but critters of some sort.

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83 SD

84 CD