Fish poop comes out as NH4, not NO3.
That is fine if you have a lower lighting/slower rates of growth.
Eg: a non CO2 planted tanks which are pretty easy if set up correctly.
It does not mean you have a plain fish only tank with cheesy gravel, lots fo aeration etc, add a few plants and expect things to go well.
Such tanks that are well set up for that method are very easy to care for due to the slow rate of growth. Fish waste tend to run low in most tanks and you do not do water changes for months, typically 6-12.
Then only after a large pruning event.
Now.........take a CO2 enriched tank, you have 10-20X faster growth rates.
Say you had 1-2 inches of fish per gallon in a non CO2 tank to supply the needed N as both NH4 and NO3.
Do a little math and you'll see that 10-20X of fish in the same sized tank is going to cause some issues.
So we use things like KNO3 instead rather than the toxic overload method with fish.
It's all about the rate of growth you want.
Water changes allow you to prevent anything from building up dosing the KNO3 without dealing with a test kit, calibrating that test kit(which few aquarists bother doing and have issues because they rely on a cheap junky test kit and assume they are correct, not hardly........).
Water changes clean the tank, allow you to work on the tank much easier etc, this is horticulture and cleaning/trimming is part of the deal, you can do it without water changes, but most everyone I know that does nice scapes, nice work using CO2 does do large frequent water changes.
Since many try to avoid the water change and thinks they can beat things by going planted, the news is you can if you use the non CO2 method.
You will have much better results doing water changes with CO2 methods though. It allows far less testing/test kit cost/yet another technique -chemical issue to address and learn about.
A water change is just much simpler.
Cry, whine, moan about water changes being hard:
Python or a DIY version makes that easy. Add ahard plumbed vavle to turn on/off to rapid 2 turns of a pair of valves to do the water change, or an autometded solenoid water changes is also easy.
I see people spends lots of time guessing the nutrients/testing/calibrating etc and still have issues (and the clown claiming to be the expert ironically) while the newbie doing the water changes wins the local Scaping contest and has far fewer issues by doing a simple routine and water changes.
Can you do it?"
Yes, you can force most any method, the real question is: are the results worth the trade offs?
Can you mitigate the trade offs?
For water changes, most everyone can.
Regards,
Tom Barr
