And I prefer to keep the O2 in my water at saturation,
not "less than".

Agreed 100 %. O2 is one of these things you can never overdose.

Lots of plants / morning / thunderstorm impending / some decaying mulm...
one would be amazed how much O2 levels can drop in just a few hours. Fish
need O2 more than they need water so to speak.

But !: (big but) Do not buy cheap air pumps as they will fail very soon.
The good ones are more expensive than you'd expect (IMHO)

Learned this the hard way.

Theo