Is there any other word in English for the algae that collect under water tank?

While "algae" is the most accurate term for the green, slimy growth that can accumulate under a water tank, there are a few other words that could be used depending on the context and the specific type of algae:

* Biofilm: This term refers to a layer of microorganisms, including algae, bacteria, and fungi, that form a slimy coating on surfaces. It's a more general term that describes the overall microbial community rather than just algae.

* Slime: This is a general term for a soft, viscous substance, and could be used to describe the algae if it's particularly thick and gooey.

* Green slime: This is a more informal and descriptive term that specifically refers to the color of the algae.

* Scum: This term is often used for a layer of debris that floats on the surface of water, but it could also be used to describe algae that accumulate in a thick layer.

Ultimately, the best word to use will depend on the specific situation and the desired level of formality.