Related Clues:

• Tiny tank plant
• Bit of pond slime
• Single-celled lab specimen
• Kelp, for example
• Bit of aquarium scum
• Aquatic organism such as plankton
• Bit of 19-Across flora
• Bit of birdbath gunk
• Simple marine plant
• Wee bit of marine life
• Pond scum organism
• Small bit of rootless flora
• Fountain growth
• Bit of 30-Down life
• Bit of fish tank growth