This is how I gauge when to do water changes, although I also check pH for that reason.
If pH is 7 right after a water change, but drop to 6 in one week, to me that means allowing one full week between water changes is too long, which is why I did a 30-40% water change every other day over the last year.
My nitrate goal is 5ppm, and a pH drop of "no more" than 0.4 between water changes,
But of course as fish grow that schedule will need to adapt to waste output as they grow.
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I set up the 180 gal Panamanian biotope tank (above) about a year ago with almost the same stock it has today.
Since that time, many of the fish have doubled (or at least gained another 3rd ) in size, even though I feed only 2 out of 3 days.
The plants aquatic and terrestrial have flourished, but I now do smaller "daily" water changes to maintain nitrate at my goal of 5ppm.
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Over the year cichlid territorial disputes have eliminated at least 4 o fthe dozen Andinoaara I started with, and a friend managed to catch an Eleotris goby nearby, added to the tank 6 months ago, that went from 6" to now nearly a foot in a very short time, straining the plant to fish waste use ratio.
These hefty bottom dwellers add quite the nutrient load quickly.
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Being near the OPs window should help that Pothos take up plenty of nitrate, and the roots should fill in nicely.providing cover and interest.
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I find almost any tropical, terrestrial plants to be great nitrate suckers, and add plenty of visual appeal outside the tank..
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