Water changes are they really necessary?

[Intuos]

@JettsPapa I know that people do it that way, but it's not something I would do personally, have been keeping my tanks for the same way for the last 30 years and it's what works for me. 

[Lowells Fish Lab]

I was thinking about this recently. Breeding is what I've come to enjoy most so about half my tanks are beyond overstocked and I have to change water in those several times a week. I can't say I don't push the limits sometimes when I've had a hard work week but I would say that watching the same groups of fish day in and day out, sometimes you just know something isn't right. People are amazing at pattern detection and when something is off, we just know. When I feel like something is off with a tank, I usually find it to be higher in nitrates than I'm comfortable with. I really do believe that fish are happier, if just a bit happier, with almost no nitrates in the water. That's just my completely intuitive opinion.

The other half of my tanks hold breeding adults and are what I would consider understocked. I load those up with plants and change water much less often because in the short term, I don't feel like I have to.

At the very end, with other factors of maintenance aside, I can think of one good reason that changing water on at least a semi-regular basis is a good idea for most people. That is keeping tank water relatively similar to tap water so that if 6 or 12 months down the road when you do find a reason to change water, you aren't introducing water with radically different parameters. My water changes seasonally, and radically, but in any case I think that water left in an aquarium can change quite a bit over weeks and months from when it came out of the tap.

[Streetwise]

Local water parameters really make this a complicated topic.