The 4th Key to good Spa & Hot tub water care is Water Testing.
In other words, YES, you do have to regularly & periodically test the water. Never judge the quality & condition of the water by just its looks or odor, although those are both excellent ways to help judge it.
Let's face it, water testing is simple. It doesn't & shouldn't take more than 2 minutes. And in that 2 minutes, you'll learn a lot about how well your spa is doing.
Here's the video: