Re: Nitrates

["Jim Seidman" <js4 at seidman_net>]

Shireen Gonzaga <whimbrel at comcast_net> wrote:

>Thanks, Chuck. If that's the case, I'm in trouble. My
>tapwater, according to the water company is 1.0 to 1.7
>ppm NO3-N. My LaMotte kit measured 2ppm, close enough
>to match the water company's numbers. That translates
>to 2*4.4 = 8.8 ppm NO3. My tank water NO3 gets even
>higher due to fish food and I've measured as high as
>26 ppm NO3.

What kind of plants and filtration do you have? In my tank (low-tech, no
CO2 injection) I have a hard time keeping NO3 levels *up*. My plants
want to consume nitrogen faster than I add it with fish food. So I'm
wondering how densely planted your tank is and how fast-growing the
plants are.

>At the advice of Scott H, I'm going to start increasing
>my kH with baking soda, since it's only 2.0 in the tank
>(according to the tetra test kit). My pH (also measured
>with tetra) in the tank is 7.6. Hopefully the increased
>kH will stimulate more carbonic acid production to lower
>the pH. Right? Or am I completely misunderstanding it?

Unfortunately, it doesn't work that way. Baking soda (a.k.a sodium
bicarbonate) will push your pH towards 8.4. It will also make it harder
to lower your pH by adding other acids. If you load up on a lot of
bicarbonate, and then add other acids, some of the bicarbonate will
indeed turn into carbonic acid, which will then turn into CO2 and be
consumed by plants, leaving the pH at 8.4 until you add so much acid
that you neutralize the bicarbonate.

On the other hand, if you add CO2, some of that CO2 will react with
water to form carbonic acid. (CO2 + H2O <--> H2CO3, meaning that CO2 and
water turn into carbonic acid and vice versa.) So adding CO2 will lower
your pH. But the more bicarbonate you add, the less effect on your pH
adding the same amount of CO2 will have.

>This is all very confusing. When folks on this list talk
>about NO3, especially Tom, is it NO3 or NO3-N?

In my experience, most people are talking about NO3 rather than NO3-N.

>If it's the former, my tapwater NO3 is really high. Have
>others checked their tapwater NO3? Is the Baltimore City
>water supply an anomaly, or do others also get high NO3?

I wouldn't call 8.8 ppm NO3 "really high." U.S. law allows up to 10 ppm
NO3-N, meaning 44 ppm NO3, in "safe" drinking water. Out here in the
Midwest, water supplies from wells or rivers often have a lot of
agricultural runoff that really pushes this limit.

I live near Chicago and get my water out of Lake Michigan, so it comes
with about 1.5 ppm NO3. But just a few miles away are people on well
water with numbers that make your 8.8 ppm look low. Getting water with
25 ppm NO3 is hardly unusual.

>If you have NO3 test kits not made by Hach or LaMotte,
>could you please look at the fine print and let me know
>if the measurements are in NO3 or NO3-N?

The SeaChem test kit reports in NO3. Its instructions do explain how to
convert to NO3-N by dividing by 4.4, but the actual reading is NO3.

Hope this helped!

- Jim