made we wonder if you could plop a clam in a nano tank as the main filter.
Unlikely main, but supplemental - could be, if the tank is large enough to house a BIG clam or several medium-sized. They will provide no mechanical filtration for a larger particles, and will not replace activated carbon, IMHO.
mwp kept 10+ T. maximas in 24g Nano-Cube as an addition to caulerpa forest.
I bought 2 baby Maximas for 10-20g tank with the same thought in mind, it didn't work for me - no noticeable effect, comparing to clamless tanks. Plus they will grow big fast. I added "jewel box" oyster as an additional filtration, at least it stays small and do not require bright light, also no noticeable difference.