Agree with esoxlucius, once the tank is cycled,, the only way to judgeis to test for ammonia and nitrite.
If there is enough media, before and after after a water change, tests will be negatice,
if there is a trace of ammonia, after a wa6ter change it may be due to the addition of chloramines (but only a trace, abd soon ofter, the media should take care of that trace).
The only measurable componant, is testing nitrate.
With an adequat schedule.....
If after a regular water change routine, nitrate concentration should no higher than 5 ppm.
If not, ...either that water change routine is not frequent enough, or not enoughwater is being changes.
You can supplement a lax routine by using heavily planted refugiums, tanks, or terrestrial growth.
When using onnly standard biomedia,
I determined thru a series of tests (that with my average stocking levels, for medium size, long lived cichlids)
my tanks needed every other day 30% to 40% water changes to maintain safe nitrate levels to prevent diseases like HITH, and hypoxia
.
Exposure to Nitrate Increases Susceptibility to Hypoxia in ...The University of Chicago Press: Journalshttps://www.journals.uchicago.edu › doi
By employing heavily planted refugiuns, I could reduce those water changes by about 2/3rd per week..
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But each aquarium has its own set of needs, so a series of tests are needed to determine what those need sre.
If one keeps short lived air breathing Anabantids, or tetras that max out at only 3 years, chronic diseases may not be a concern.
But if the goal is to maintain long lived cichlids, such as oscars, Geophagines or severum that are prone to HITH (if kept in conditions such water pH or hardness)
not evolved to resist chronic pathogenic bacteria in), then nitrate reduction becomes much more of a cercern