If I was thinking like that, I would never change my water... My CO2 injected tank is so heavily planted that I need to ADD nitrates and phosphates, or theses levels tend to naturally lower over time, even if I'm overstocked...
So according to water tests and low algae growing, I can tell the water is "clean", but it may not be "quality" water, as some nutrients will lack.
Also, it doesn't mean because ferts (NO3, PO4) are low that the water is "quality water". The TDS could be high, water with high cooper is bad for inverts, water with ultra high KH and GH may not be so good for some tetra by example...
Sometime the tap water TDS are so high, even if there's no nitrates/phosphates, aquariums keeper must use RODI unit then remineralize this water...
Usually the tap water is good for almost all fishs, there's some specific regions where's the water isn't good for fish tanks.
I still struggle with water quality even though my parameters are go and I do weekly 50% pwc. Thank you again!
