What should I put in a 6 gallon tank?

I gave up on the idea of using it earlier. I just recently discovered the filter I thought was broken actually works perfectly fine, its a small hang over the back filter. Should I even bother using the tank for anything? I already have everything to take care of fish because I have a 55 gallon aquarium... show more I gave up on the idea of using it earlier.

I just recently discovered the filter I thought was broken actually works perfectly fine,
its a small hang over the back filter.

Should I even bother using the tank for anything?

I already have everything to take care of fish because I have a 55 gallon aquarium also.
I have a heater for it and a thermometer and the filter, as I mentioned.

I don't think its big enough for a betta, could I use it as a breeding ground for brine shrimp to feed to my fish?
Idunno, sounds kind of cruel and my mum might not want me to have it in my room.

Thoughts guys?
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