Serial Dilution

[joannde]

I'm trying to get a handle on my super duper extra high nitrite readings so I did a serial dilution - I'm a little confused by the results so I thought I'd come here and confirm that I did this correctly

1. Full strength tank water
Nitrites - dark purple - looks like its not as dark as 5ppm but I guess it was

2. 1/2 cup tank water, 1/2 cup tap water (tap water nitrites is 0) = 1/4 tank water
Nitrites - dark purple again - same color as above

3. 1/2 of the mixture from step 2, 1/2 tap water = 1/8 tank water
Nitrates still look the same color to me

4. 1/2 of the mixture from step 3, 1/2 tap water = 1/16 tank water
Nitrates at 0.50

0.50 x 16 = tank water is 4.0 ppm

BUT if that were true wouldn't I have shown a nitrite level of 1.0 in step 3 ??? and a nitrite level of 2.0 in step 2 ????

(and I thought I was good at math ! HA !)

 

[cplawrence]

Your overall logic is correct, although your math is a little hazy:
1) First dilution:
1/2 cup tank and 1/2 cup tap = dilution by a factor of two.

2) Second dilution:
1/2 cup first dilution and 1/2 cup tap = dilution by a factor of four.

3) Third dilution:
1/2 cup second dilution and 1/2 cup tap = dilution by a factor of eight.

If the third dilution gave 0.5 ppm, the tank water is 4 ppm. However, you are correct that the second dilution should then have been 1 ppm and the first dilution 2 ppm. Not sure what could have happened here. The only thing I could think of is to test the water you were diluting with.

In any case, I assume that you are doing a fishless cycle. If that is the case, you may want to do a water change to bring the nitrite down a bit--if it is too high, the cycle may tank longer.

 

[joannde]

thanks - we both came to the 4ppm number so I can only assume we're both correct !

Thankfully it IS a fishless cycle - and I just did a 70% water change.

I did a test on the resulting tank water but had to do another serial dilution because I couldn't figure out the results again !

1. tank water - unreadable - HIGH

2. 1/2 tank , 1/2 tap = somewhere around 2 -so difficult to tell !

3. 1/2 of above and 1/2 tap = 0.5ppm nitrites

Tank nitrites post water change is therefore = 2.0ppm (please correct me if I'm wrong)


I did a 3rd dilution as a test and the reading was .25, so I'll assume that I'm just unable to read the colors between 1ppm and 5ppm !!!!

Thanks for helping me confirm my math. I'll leave the tank at 2ppm and hopefully the cycle will restart.

Cheers !