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Rescuing A Fish In Cycle Gone Wild - Part Il

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Fish Connoisseur
Dec 31, 2004
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Part II


If you are determined to ignore the above advice in Part I and still think you want to proceed with a fish in cycle, then you need to be aware of the information presented below.


Ammonia in water exists in two forms. NH3, which is the familiar nasty gas we know. Fish exhale NH3. Rotting organic matter will also create ammonia. This stuff is highly toxic and will definitely be harming fish by the time it reaches a concentration of .05 ppm (Some fish and inverts need even lower levels to be safe). However, most of the ammonia in water exists in the form of ammonium which is NH4. This is way less harmful. But in sufficient concentrations and/or exposure times, it causes external burns. The typical test kits we use measure Total Ammonia (TA) which is the sum of both NH3 and NH4.

Knowing how dangerous any level of TA might be requires that one know not only how much total ammonia there is but also how much of that total is in each form? The answer depends upon two other water parameters- pH and temperature. The higher the pH and/or temperature, the more of the TA that is in the toxic NH3 form. To calculate how much of the toxic NH3 form of ammonia requires that you know what the pH and temperature of your tank water are. Once you know all three numbers (total ammonia, pH and temperature) there is a formula for calculating how much of the total ammonia is in the form of NH3. It is way more complicated to use than most of us can handle. Fortunately, there are charts and tables available for this calculation. There is also currently a handy dandy ammonia calculator you can find here: http://www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php

1. Choose NH (NH3 + NH4)*
2. Enter in the total ammonia reading from your test, choose ppm.
3. For a fresh water tank, enter 0 for the salinity.
4. Enter your tank’s current pH.
5. Enter your tank temperature and choose F or C, whichever applies.
6. Click Calculate.

The number you want to know is the one for NH3.

[* If your kit measures ammonia as nitrogen aka –N, choose NH-N (NH3-N + NH4-N) in step 1. above.]

Why do you want this number? Because, to get a tank cycled you need to have ammonia (and nitrite) present and you want to have as much total ammonia present as possible without causing permanent harm to the fish. And it is the NH3 that will cause the real harm. Your goal is to allow the total ammonia to rise as high as possible as long as the NH3 content does not get to .05 ppm using that calculator. And even if that level of NH3 is not reached, there is still a limit to how high one can allow total ammonia to rise.

Remember, NH4 can still cause ammonia burns. This writer’s normal cutoff for total ammonia for more than a few days or so is 2 ppm. As a rule of thumb, you can run at 2 ppm of total ammonia with the NH3 being well under .05 for some short amount time. The lower it is under .05, the better. At under .02 ppm of NH3 many fish can be in up to 2 ppm for a number of days and still be OK. The best sign of how long is how the fish behave. If they act distressed, then that is high and/or long enough. Some fish can manage in higher levels, others can’t. This is why you must also watch the fish as well as the test levels.

Hint: As a rule, problems from ammonia become increasingly serious as one’s pH goes above 8.0 and by 8.5 one must really be doing a fishless cycle only. This is very relevant for those keeping rift lake cichlids

There are two goals in fish in cycling which are diametrically opposed. One is to allow ammonia and nitrite to get high enough to get the cycle done as quickly as possible. The other is to keep the ammonia and nitrite from being high enough to cause permanent harm to the fish. Every water change slows the cycle. But the failure to do one at the proper time can harm or even kill the fish.

Fish will not behave as they normally do. Signs of ammonia poisoning can include sluggish behavior, panting, and gill discoloration (gill burn). Fish may hang just below the water surface or they may hide or stop eating. When you know you have ammonia in the tank during cycling and you notice such behavioral changes, the best course of action, regardless of test results, it to do an immediate water change of 50% or more.


This too is a problem and it is important to understand how it affects fish in order to know how you can deal with it.

Nitrite enters the bloodstream through the gills and turns the blood to a chocolate-brown color. Hemoglobin, which transports oxygen in the blood, combines with nitrite to form methemoglobin, which is incapable of oxygen transport. Brown blood cannot carry sufficient amounts of oxygen, and affected fish can suffocate despite adequate oxygen concentration in the water. This accounts for the gasping behavior often observed in fish with brown blood disease, even when oxygen levels are relatively high.2

Fish will not behave as they normally do. Because their blood is not carrying oxygen, fish will behave as if they are suffocating. They may hang just below the water surface or near filter outflows trying to get air. What you will not see is any outward sign of bodily damage nor damage to the gills of the fish.


Fortunately, there is an effective way to blunt the harmful effects of elevated nitrite that doesn’t involve changing lots of water- you add salt (sodium chloride) to the water. The chloride in the salt acts to” block” the ability of nitrite to enter though the gills of the fish and thus to cause the harm inside the fish it might. So it is possible to manage elevated nitrite over the short term using salt in relatively small amounts.

Sodium chloride (common salt, NaCl) is used to “treat” brown blood disease. Calcium chloride can also be used but is typically more expensive. The chloride portion of salt competes with nitrite for absorption through the gills. Maintaining at least a 10 to 1 ratio of chloride to nitrite in a pond effectively prevents nitrite from entering catfish. 1

It should be noted that the Merck Veterinary manual suggests a lower ratio of chloride:

“In freshwater production ponds for channel catfish, a ratio of 6 parts Cl to 1 part NO2 has effectively prevented or treated methemoglobinemia caused by nitrite exposure.” 2

Since the amount of salt needed to produce either 6 or 10 times the chloride as nitrite is minimal, this author prefers to use the higher ratio of 10 to 1 in order to be more certain of obtaining the needed relief. One should also be aware that studies indicate that, whether one changes water or uses chloride to counter the effects of nitrite toxicity, it will still take between 24-72 hours for nitrite already inside fish to be completely eliminated. Preventing further nitrite from entering usually solves the problem.

Plain old table salt is just fine for use here. Do not worry if it says Iodized or if it says it contains Anti-caking agents. The amount of either of these in the salt is so minimal one would pickle their fish long before these ingredients would be doing any harm. Read here for facts about table salt and fish: http://www.theaquariumwiki.com/The_Salt_of_the_Earth

The problem with dealing with elevated nitrite is that the typical aquarium kits do not go high enough to let us know how much nitrite may really be in any tank. And this makes fish in cycling more complex and more work than fishless. You will likely need to know how to do diluted nitrite tests. For this you need a way to create an accurate mix of your tank water and some amount of pure water, i.e. distilled or reverse osmosis/deionized (ro/di) water. You should be able to find a gallon of distilled water in the supermarket. Some fish stores sell ro/di water.

You will need a clean measuring cup as well. You will use this to mix different solutions of tank and pure water to be able to test for nitrite. You do not want to use your tap water for dilution purposes as it will often contain things that can cause test result be inaccurate.
The reason for using a measuring cup is that it is important to get the proportions of the mix as close to dead on as possible. The advantage of measuring using a cup from which you will only use a few ml is that the potential for mixing errors is way less of an issue in 8 ounces than in 5 or 10 ml of water. What you will do is start by making a 50/50 mix (4 ounces each) of tank and pure water. Then you pour 5 ml of this into the little test tube and then do the nitrite test. Multiply the result of the test by 2 to get the actual ppm in your tank.

However if this 50/50 diluted test result is still at the kit’s maximum level and the test kit reads to a maximum level of 8 ppm or less, you will have to do another dilution. The easiest way is to start with ¼ cup of tank water and ¾ cup of pure water. Test this mix and multiply the result by 4 this time. Alternatively you can use ½ cup of the initial 50/50 mix and then add ½ cup of pure water to this. The result will also be ¼ tank and ¾ pure water. If this test is also at the maximum number, don't worry about a further test, just do a huge water change (at least 50%) ASAP. After doing the water change, test for nitrite and then add the required amount of salt to deal with that amount of nitrite.
You will need to continue testing for nitrite because any further rise may mean that either water changes are needed and/or that further salt additions are needed.


PPM is a measure of concentration in water. You cannot weigh ppms. However, 1 mg/l is almost the exact equivalent in water to 1 ppm. So one can use ppm and mg/l interchangeably in this case. You can weigh milligrams.

To add 10 mg/l of chloride for every ppm of nitrite in the water, use the following steps:

1. Multiply your nitrite test reading by 10. This will give you the needed mg/l of chloride you need to add.

2. Calculate the actual volume in litres of the water in your tank. If your volume is in gallons you must convert this into liters. (As a rule, using the advertised volume of the tank at about 85% will put you in the right ballpark.) 1 gallon = 3.875 litres

3. Multiply the number in #1 above by the number of liters of water in #2 above to get the total number of mg of chloride you will need to add.

4. Because salt is roughly 2/3 chloride, you must multiply the number calculated in #3 by 1.5. You now know how many mg of salt you should add to the water. Dividing this number by 1,000 will convert this amount to grams which are easier to weigh for most people.

5. Do not add the dry salt directly to the tank. Remove some tank water to a container and mix the salt in that, then add the salt water to the tank spreading it around the surface.

Hint: We have calculated a handy conversion from grams to volume so one can measure in tea or table spoons which most folks are likely to have while a gram scale is not. The following calculations were made using an Ohaus triple beam scale: ¼ teaspoon of salt shaker sized table salt weighs 2 grams.

The readings used in this article are for API and similar type test kits which measure in total ions. Some kits will measure using a different scale, they are only measuring the nitrogen ions. You can tell when a kit reads just the nitrogen ions by the way they state things. The typical kits will say they measure Total Ammonia (NH3 + NH4), Nitrite (NO2) or Nitrate (N03). Kits that measure only the nitrogen ions will usually say they measure Total Ammonia-Nitrogen (NH3-N + NH4-N), Nitrite-Nitrogen (NO2-N) or Nitrate-Nitrogen (NO3-N).

Just like one can convert distances between miles and kilometers, one can convert between the total ion scale and the nitrogen ion scale. Since this article is using the total ion scale, if you have a kit that reads in –Nitrogen (-N), you must multiply your results as follows:

1 Nitrite in Fish Ponds
June 1997
Robert M. Durborow 1, David M. Crosby 2 and Martin W. Brunson 3

2 The Merck Veterinary Manual for Veterinary Professionals
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