Rate of Nitration

[hopeful1]

Is there any general idea, based on the number of fish and the size of the tank, regarding the rate of Nitration, without intervention?

 

[CT_]

Do you mean how much ammonia/bioload the tank can process into nitrate?

Assuming you have enough surface area in your tank and filter(you probably do unless you don't have a filter or substrate/decor/plants) it'll process as much as you want assuming you don't change how much food you add suddenly.

[hopeful1]

Yes Please excuse my thinking normally the entire process would follow suit and I am assuming the normal process here. I am kind of relating to the degree of saturation indicated by the API test kit.

Normally water changes could hold nitrates at bay, but I am trying to get an idea of how fast  the process might create nitrates. For instance if you do a 25% water change, will the process red line next week before the water change based on my number of fish?

I changed over 60 gallons of purified water in a month in 40 gallon tank. The most I have done is 15 gallons at a time, mostly 10 gallons at a time, while vacuuming everyday, adding rocks, and plants under and above water (pothos).

In my tank nitrites do not register, because of so many water changes, however I am stuck with nitrates. I may try a 40% water change soon, and adding a substrate (at which I am a raw beginner). My fish are happy and strong thrilled with brine shrimp.

What is the worse case contamination of 12 fish in 40 gallons?

 

[CT_]

Ah.  Well nitrites will all go to nitrate on a cycled tank so you really shouldn't see nitrites.

 

The steady state nitrate level will be inversely proportional to the size of your water changes and proportional to how much you feed(assuming a fixed water change and feeding frequency and ignoring the contribution of plants absorbing nitrogen).

 

So if you double your feeding you double your nitrates (once things settle).  you double your water change volume you half your nitrates (again once things settle). 

[HH Morant]

Every tank is different because of the number of fish, the size of the fish, how much food goes into the tank, how many plants, etc. It is not really possible to do a calculation, so people decide how often to do water changes and how much water to change by testing the water to figure out when a water change needs to be done. By testing the water you will learn how much nitrate your tank generates and how often you need to change the water (and how much) in order to keep the nitrate level where you want it.

Lots of people do 50% water changes, so that is not extreme. I often do 67% water changes.

If you do smaller water changes, you will need to do them more often. If your test shows 80 ppm nitrates and you do a 10% water change, you still have 72 ppm nitrates. 

Your water change routine may need to change over time if your fish are growing or you increase the number of fish, so you should test occasionally to make sure your water change routine is resulting in the nitrate level you want. Periodic testing also helps warn of ammonia/nitrite problems, which can happen unexpectedly.

[Ken]

See if this helps.

https://www.aquariumcoop.com/pages/water-changes

[CT_]

On 8/7/2021 at 2:06 PM, HH Morant said:

It is not really possible to do a calculation, so people decide how often to do water changes and how much water to change by testing the water to figure out when a water change needs to be done.

While I agree with your general point, you can absolutely do calculations.  Math is wonderful and people discount it too much.  Nitrogen is a great example because it's a conserved quantity so its fairly easy to model.  If you add plants its hard to account for where that nitrogen goes in plants but it still gives you a conservative bound on water changes. 

 

Also before someone says you can never be exact, models and calculations don't have to be exact to be useful.  If they did we'd have no engineering.

 

On 8/7/2021 at 2:06 PM, HH Morant said:

If you do smaller water changes, you will need to do them more often. If your test shows 80 ppm nitrates and you do a 10% water change, you still have 72 ppm nitrates. 

You just did a calculation 😉

Edited August 7, 2021 by CT_
edit for clarity