Page 40
Copyright Wet Paper Publications 2010
P
ROJECT
2.6 T
ESTING WATER
FOR
N
ITRATES
Background
Nitrate ions (NO
3
-
) are produced in an aquarium as a result of
deadly nitrite ions (NO
2
-
) being oxidised by bacteria.
The chemical reaction which occurs is shown below:
NO
2
-
+ H
2
O
NO
3
-
+ 2 H
+
(Nitrite) (Nitrate)
The nitrite ionsNO
2
-
formas bacteria oxidise ammonia excreted
by aquatic and marine animals.
Nitrobacter species of bacteria were given credit for this
conversion in aquaria however recent research suggests that
Nitrospira sp
may be responsible for nitrite conversion to
nitrate. The conversion occurs in the biofilter of the aquarium.
Historically, nitrate was considered harmless to fish as it is far
less toxic than ammonia or nitrite. While lethal levels may be in
the area of 1000 ppm, the effects of lower levels on long term
health of aquatic and marine animals are not well understood.
Certainly the sensitivity of different species to nitrate levels
varies, and it is a good idea to avoid any potential long term
effects ongeneral health, growth andbreeding abilitybykeeping
levels low.
Nitrate levels should be kept below 50 ppm to avoid long-term
health effects, but levels below 25 ppm should be aimed for.
Fish which have been aquarium bred for generations are more
likely to tolerate nitrates better than wild captured fish.
Natural environment
In a healthy natural aquatic environment there is little or no
detectable nitrate. Nitrate accumulates in an aquarium in
proportion to the number of stock and is a good indicator of
general water quality.
As nitrate levels increase, water quality decreases.
• The quantity of permissible nitrate varies with the particular
aquatic life being cultured.
• For systems growing fish, acceptable levels are 20 to 40
ppm.
• Many species of marine fish will accept higher levels of 80
to 100 ppm with little effect on their health.
• It is recommended that when levels climb above 40ppm
steps should be taken to lower the nitrate and avoid stress.
For reef systemsmuch lower levels of nitrate are needed. A level
of 5ppm or less is optimum. Again, many invertebrates will
tolerate higher levels but once these levels climb above 20ppm
many of the more sensitive invertebrates will be injured or die.
It has been shown that small quantities of around 5ppmof nitrate
are of assistance in culturing marine plants.
The easiest method to lower nitrate is to change water. Regular
water changes should ensure that nitrate levels stay within the
acceptable limits.
- Recommended minimum water change requirements are
25% per month. If water changes do not keep the nitrate at
acceptable levels then your stock load maybe too great for
your aquarium system.
Denitrification filters can lower nitrate successfully, but this
must be closely monitored to avoid dangerous gases that can
harm aquarium inhabitants.
Marine plants and algae can use some nitrate as nutrients and are
a great way to control nitrates.
Materials
• Aquasonic
(TM)
Nitrate test kit (Figure 40.1) or similar
Procedure
Step 1 Rinse a clean test tube and it's cap several times in
water to be tested.
Step 2 Fill the test tube to the 5, 10 or 20mlmark.When testing
5 or 10ml samples, distilled water has to be added to
reach the 20ml mark. The test has to be timed.
Step 3 Add 7 drops of reagent 1.
Step 4 Add 1 tablet of reagent 2, cap and shake vigorously
(tablet takes approx. 2 minutes to segment).
Step 5 Open test tube and leave it stand for 5 minutes.
Step 6 Add 7 drops of reagent 3 and 7 drops of reagent 4, cap,
and invert several times.
Step 7 Open test tube, wait 3 minutes, then compare with the
colour chart. Place the test tube on the white portion of
the colour chart, below the closest matching colour.
View vertically to compare the test with the colour
chart.
Step 8 On completion of the test, rinse clean the test tube and
cap.
Aquasonic
Figure 40.1 Nitrate kit
The water quality monitoring tables on
Pages 107-111 allow you to record your
data over a number of weeks.
1,2,3,4,5,6,7,8 10