Nitrate Testing/Chemistry question

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Watcher74

Watcher74

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I have testing kits from Aquarium Pharmaceuticals, Inc. In the directions for the NitrAte test it states:

"This test kit measures nitrate as nitrate ion or "total nitrate"(NO3-). Other nitrate test kits that measure "nitrate-nitrogen" (NO3-N) will give readings 4.4 times LESS than this test kit."

So the often quoted suggestion of keeping your NitrAtes below 20ppm is now meaningless without further clarification on what nitrate test to use.

In my 29 gallon tank that I keep on a strict maintenance routine that includes cleaning the filters every week I still have to do at least 2-25% water changes a week to keep the Nitrates down below 20ppm.

Inhabitants:
1 2" angelfish
1 2&1/2" Boesami Rainbowfish
2 1&1/2 " Dwarf Neon Rainbowfish
3 2" Cory Julii

I feed very carefully and can see no detectable food waste in the water changes even though I vacuum the gravel. I read about people that only do 25% water changes every two weeks and never reach 20ppm nitrates.

So which is it? Below 20ppm of (NO3-) or (NO3-N)?
 
daveedka

daveedka

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I'm no chemist so I'm sure you'll get better answers, but the total nitrate is what we test for NO3. Also remember that the nitrate test is used more as an indicator of total pollutants. In other words we assume if we have high nitrates we have high levels of things that aren't as easy to test, thus water changes are necessary tokeep levels low. In a planted tank a good bit of the nitrate is consummed by the plants so a water change routine is more important than the testing as there is no easy way to verify pollutant levels.
 
Watcher74

Watcher74

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Yeah, I understand that we are removing far more things than just nitrate when we do partials for the benifit of our fish, as well as adding natural buffering, but why am I having such a hard time keeping the nitrates down?

I read in a thread here a few weeks ago where someone was saying something like, "I'm pretty lax about maintenance compared to most people on here. I only do a 25% partial every two weeks and my tank has never reached 20ppm of nitrates." So how come I have to change 4 times as much water to achieve the same results?

I just tested my tap water and there was no detectable nitrates in it.
 
kveeti

kveeti

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Originally posted by Watcher74
So how come I have to change 4 times as much water to achieve the same results?
Click to expand...
So many variables: stocking level and type of fish, amount fed, live plants, amount of live plants...
 
Watcher74

Watcher74

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In my 29 gallon tank that I keep on a strict maintenance routine that includes cleaning the filters every week I still have to do at least 2-25% water changes a week to keep the Nitrates down below 20ppm.

Inhabitants:
1 2" angelfish
1 2&1/2" Boesami Rainbowfish
2 1&1/2 " Dwarf Neon Rainbowfish
3 2" Cory Julii

I feed very carefully and can see no detectable food waste in the water changes even though I vacuum the gravel.
Click to expand...
Unplanted. What other variables do you need?
 
R

RTR

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Fish stock, feeding levels, and substrate size and depth are the variables.

When I had the mbu puffer, I was hard-pressed to keep the water below 40ppm total nitrate. But when you have a >2' very heavy-bodied predator, you have to expect high maintenance. I'll never do that to myself again.

Most hobby test kits report total nitrate. Some kits report nitrate-nitrogen. The advantage to using ammonia-nitrogen ->nitrite-nitrogen ->nitrate-nitrogen is that the titers are then 1->1->1, whereas the total ammonia ->total nitrite ->total nitrate you have to compensate for the varying molecular weights of the nitrogen-containing material (17 vs. 46 vs. 62, while the nitrogen in each of those is 14).

Generally, if only the words ammonia, nitrite, or nitrate are used, the reference is to the whole molecule or ion. If you refer to the ammonia-nitrogen, nitrite-nitrogen, or nitrate-nitrogen, you have to so specify by using the correct term.

HTH
 
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Watcher74

Watcher74

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RTR, that's too much for me.

Can you clarify slightly please? Any opinion based on the facts I have given or what I need to add to give a guess?
 
happychem

happychem

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If you're not fertilizing with NO3 as some planted folks do, then the amount of nitrogen in your system is an indicator of biological activity, namely, the amount of wastes being produced. Since a cycled tank should have no NH3 or NO2, we measure NO3.

So, you want to know the amount of N in the form of NO3.

If you measure nitrate-nitrogen, then, as the name implies, you've measured the amount of nitrogen in the form of nitrate.

If you measure total nitrate, then you have 1 other thing to consider, oxygen. NO3 is 1 N and 3 O's, it has a molecular mass of 62. N has an atomic weight of 14. So N makes up about 22% of the weight of NO3.

Or, 4.4 times higher than something that is just measuring the N.
 
R

RTR

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The point that I was trying to make is that the total xxx tests appear irrational, as 1ppm ammonia does not result in 1ppm nitrite and 1ppm nitrite does not result in 1 ppm nitrate - the test meaures are in weight per unit volume and the weights of the three materials are different. The scale would be somthing like 0.8 ->3.3 ->4.4 (but don't hold me to those figures, I did not calulate that, just guestimated)

But 1ppm ammonia-nitrogen will result in 1ppm nirtite-nitrogen and finally in 1ppm nitrate-nitrogen.

But the test ranges used in the hobby kits are selected based on the toxic ranges of the three materials, not material balances.

Edit: It should have been 1.2->3.3->4.4. I should know better than ro do math in my head.
 
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Watcher74

Watcher74

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That I can understand, thanks for the clarification.

You too happychem.

Does anyone, though, have any idea why my nitrates are so hard to control?

I have small gravel approx. 1 -> 1&1/2 deep.

I believe with my current fish load I have a slightly understocked tank, yes? Especially with the current size of the Angelfish.

I'm trying to figure this problem out so I can correct it. Or at least understand why it exists.
 
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