Odd nitrate readings
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Old 03-13-2013, 08:53 PM   #1
Rainer
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Odd nitrate readings


The nitrate reading in my 29g after the 50% WC on Sunday was 5-10 ppm. I dosed half the standard EI amount, 1/8 tsp (1 dash) of KNO3, that day, then tested on Tuesday.

That reading was 40-80 ppm. I've seen similar readings with another test kit from API, and both seem normal enough when measuring non-EI tanks, so I'm hesitant to immediately blame the test kit.

Could this be old root tabs leaching into the water column? The substrate is high-CEC too.

Test error? I have two other people verify the results and I follow the directions carefully, so it doesn't seem like user error.
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Old 03-13-2013, 10:16 PM   #2
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The fact that you say 40-80 ppm as the range where you think nitrate is at is testament to how inaccurate API tests can be. but if we assume its right since on sunday you got a reasonable reading, potentially something might be leaching nutrients back into the water column. How are plants doing? If they are healthy and you have a lot, I wouldn't be too concerned as a WC and the week of growth will lower these levels.
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Old 03-13-2013, 10:30 PM   #3
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Default Re: Odd nitrate readings

I'm trying to keep the tank at 10-20 ppm for the sake of the inverts. These spikes have happened before; conversely I've had at least one midweek 0-5 ppm reading too, awhile back, so it's unpredictable and very difficult to stay in range.

It's a fine line between algae farm and invert graveyard in this tank.

Plants are in good shape except for some BBA and crinkly leaves on the sunset hygro, which is finally taking off after years of just sitting there. CO2 is as high as I dare take it and I have high flow and high O2 levels.
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Old 03-13-2013, 10:52 PM   #4
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Default Re: Odd nitrate readings

If you don't have them already, floaters should help with spikes. Same goes for nitro, sprites, etc. Fish food? Tests taken at the same time of the day? Could the WC have disturbed the substrate, root tabs?

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Old 03-13-2013, 11:04 PM   #5
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Default Re: Odd nitrate readings

It's possible the WC disturbs the substrate, especially since there's a bare area near there, but there were no visible signs of it.

I had to remove the floaters after increasing the flow to maximize O2 for the inverts.

Tests are generally taken in the afternoon, before feeding.

What's nitro?
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Old 03-13-2013, 11:27 PM   #6
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Quote:
Originally Posted by Rainer View Post
What's nitro?
Sorry, should have been 'hygro'
And just throwing some ideas out.
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Old 03-14-2013, 01:32 AM   #7
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Test your tap water every time. Tap water can have nitrate, especially if you are in an agricultural area, but even city water can have NO3 occasionally.

Try doing a water change this way:
Set up a bucket of water with an air tube in it (I rubber band a rock to the air tube to keep it down) higher than the tank.
Tie a loose knot in the air tubing.
Start a suction in the tubing, then snug up a bit on the knot. You want a steady stream, but not too much. (You might be able to handle the full flow without the knot)
Clip the tubing so the flow is horizontal, just under the water level in the tank.

Now start another air tube flowing out of the tank into a bucket on the floor. Keep the intake of this one fairly high up.

Goal: VERY slow out, matching in, and neither gets anywhere near the substrate. The water is not churned up at all in any way that could affect the substrate. Monitor the flow, and make sure the water level does not drop too much.

It may take an hour to do a water change, but then you will know that there was absolutely no way of disturbing the substrate.
Then monitor the NO3 through the week.

The small dose in that large a tank (1/8 tsp or less in 29 gallons) should not have raised the reading by enough to show as a color change between 2 colors on the test.
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Old 03-20-2013, 12:10 AM   #8
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Default Re: Odd nitrate readings

More weirdness.

Four hours after the 50% WC on Sunday (taking pains not to disturb the substrate), the readings were 0 nitrate, 0.5 ppm phosphate. I then added a full EI dose of macros.

Four hours after that, nitrate was not quite 20 ppm - in line with expectations - and phosphate was around 5 ppm.

Today, two days later, the readings were not quite 40 ppm nitrate and 5-10 ppm phosphate. Only CSM+B was added in the interim.

IMO this is consistent with slow leaching of fertilizers from the eco-complete, despite no root tabs being added in at least four months.

But does that make sense? Can a high CEC substrate really do this over such a period?

Or is something else going on?
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Old 03-21-2013, 02:39 AM   #9
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Default Re: Odd nitrate readings

Tonight, after almost four full photoperiods since the last dose, the nitrate level is 30 ppm and the phosphate is between 2-5 ppm.

At least it seems to have leveled off.
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Old 03-21-2013, 03:09 AM   #10
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Really weird... maybe try not dosing for a week or so and test everyday to see what your levels are like.

I assume that you wash your glassware the same way every time and the reagents havent gone bad.

Just my two cents.
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Old 03-21-2013, 04:21 PM   #11
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Default Re: Odd nitrate readings

Quote:
Originally Posted by homemadepopcorn View Post
I assume that you wash your glassware the same way every time and the reagents havent gone bad.
Correct on both counts. The test kit is maybe six weeks old and I'd seen similar results with the previous kit.
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Old 03-23-2013, 04:52 PM   #12
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Default Re: Odd nitrate readings

Friday evening the nitrate level was down to 10 ppm so I added a half dose of KNO3, the first since Sunday afternoon, approximately 5.5 photoperiods ago.

Phosphate was still around 5 ppm so none was added. To be safe 1/8 tsp of KSO4 was dosed (some had also been added on Wednesday).

I wonder how long it will take for these spikes to die down. I'm trying to keep within a range of 10-20 ppm nitrate but it's impossible to predict how much and when to dose.
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Old 03-28-2013, 11:54 PM   #13
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Default Re: Odd nitrate readings

The nitrate level Tuesday evening was zero, consistent with my expectations, so I added a full EI dose. There had been no spike between Sunday and Tuesday, but today the reading is 40 ppm.

What the heck is going on?
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Old 03-29-2013, 12:04 AM   #14
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Check the age of the test kit. They do expire and go bad. The crystals take more and more to break up until they solidify completely then your nitrate test will be useless
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Old 03-29-2013, 12:35 AM   #15
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Default Re: Odd nitrate readings

The expiry date is 10/2017. I've had that kit only six weeks or so. The phosphate kit expires in 2015.
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