Related Clues:
- Floor plants?
- Unwanted stuff in a fish tank
- Producers of oxygen
- Riff-raff making unpleasant film
- What jam makers skim
- Unwelcome pool growth
- Pool film
- Growth in a neglected pool
- Nori or spirulina, e.g
- Buildup in a fish tank
- Fish pond growth
- Froth, foam, dross
- Neglected aquarium's accumulation
- Layer on a stagnant pond
- Red-tide contents