Tank size & Maintenance - Cherry shrimp

Hi everyone,
Just wanted to ask a few questions about your tanks and maintenance.

I currently have a 3 gallon cube. It's been set up for about a year now. I'm not sure what I am doing wrong, but I can't seem to get it to "thrive." I always have maybe.. 6 shrimp in the tank but they don't seem to live long or reproduce fast.

I tend to do a small water change once per week.. should I stop this? Am I making the water parameters fluctuate too much?

What all are you doing to have thriving tanks?