Fishless Cycle: Something Fishy About Api Test Results

[Jeremy180]

Okay, so when I first  started my cycle a month ago, I followed the recommendation of the calculator on this site and placed 6ml of 10% ace hardware brand ammonia in a 29 gal (100L) tank.
This brought the ammonia to between 4 and 8 ppm according to the API test kit.
This was on October 5th.
After being informed by daizeuk that 5ppm was too high, I did a 50% water change on the 12th of October, thus bringing the ammonia down to between 2 and 4ppm.
During this water change, the aqueon filter that came with the tank quit working...
So I took the filter and heater (which had been making a knocking noise) down to the LFS to get them serviced, and they were very accommodating, even printed me out a new receipt to replace the one I'd lost. 
The funny thing is that to "fix" the filter, the employee took it apart, but he couldn't find anything wrong Then when he put it back together, he tested it in a stock tank in the back, and it worked perfectly!

Next came the heater, which never once made a sound at all while he was testing it...

Despite this, the heater was switched out for a new one, and the new heater has been very silent.
 
I probably should have been more vigilant with the testing after this, because I had just been testing for nitrites in an effort to conserve test formula, and I'd also only been testing about once a week.
Well, today I finally gave in and tested ammonia, which was between 0 and .25 ppm 

 Assuming  I'd missed the nitrite spike due to spotty testing,

I did a nitrate test and found it to be between 10 and 20. ppm!

But  then it hit me:
How on earth could one get 10-20ppm nitrate from about 3ppm ammonia?

So I re-test the aquarium water and get the same result.
Still not convinced, I take filtered water from the refrigerator and test it as a control, and get 0 ppm, as expected if the nitrate test was working properly.
BUT...
HOW?!!
I know for a fact that there couldn't have possibly been more than 5 ppm of ammonia in the tank at any one time, so how could there now be 10-20 ppm nitrate?

 

 

[Fishmanic]

there is not a 1 to 1 correlation between ammonia and nitrate--you're test is probably accurate---the nitrates show that nitrites are being converted to nitrate so your cycle is coming along.  You probably missed the nitrite spike.  To know if you're now cycled, you should redose ammonia to about 3 ppm and see if ammonia and nitrites drop to 0 in 24 hours.

 

[Jeremy180]

there is not a 1 to 1 correlation between ammonia and nitrate--you're test is probably accurate---the nitrates show that nitrites are being converted to nitrate so your cycle is coming along.  You probably missed the nitrite spike.  To know if you're now cycled, you should redose ammonia to about 3 ppm and see if ammonia and nitrites drop to 0 in 24 hours.

Thanks, will do.
I just realized that the formula for nitrate shows that several oxygen molecules are added from the air/water, so I guess that's where the "extra" nitrate came from?
(Chemistry never was my best subject)

 

[daizeUK]

Yes, it has to do with atomic weights.  The nitrogen is 'conserved' as it is changed from one form to another by the bacteria NH3-NO2-NO3.  Hydrogen atoms are much lighter than oxygen atoms, and 3 oxygen atoms weigh more than two, so each form gets 'heavier' and therefore has more mass relative to the solution it's in.  We measure the mass in milligrams therefore NO3 will register more mg/L (=ppm in water) than NH3 for the same amount of nitrogen.  You can work out the exact conversion rates using the atomic weights of each element, can't remember them off the top of my head (!) but I'm sure TTA would tell you more

 

[TwoTankAmin]

The math, using API test kits. is roughtly as follows:
 
1 ppm ammonia becomes 2.55 ppm nitrite which becomes 3.45 ppm nitrate.
 
So 3 ppm of ammonia becomes 10.35 ppm if nitrate. This all assumes there are no live plants present and that both ammonia and nitrite read 0 when you yest for nitrate. It also presumes you have no ammonia, chloramines or nitrate in your tap water.