Using shrimp or fish food
One of the more popular fishless cycling methods is to buy a few dead shrimp at the grocery store, cut them up into chunks and add them to the aquarium. The shrimp decay, which produces ammonia to feed the nitrifying bacteria. There are a few drawbacks with this method, one being that the hobbyist really has no way to know how much ammonia is being produced by the decaying shrimp, and the aquarium does not look very good with dead shrimp laying on the bottom. Also, the organic material of the shrimp can cause bacteria blooms which turn the aquarium water cloudy. This method works but it takes time and patience and you will probably see a spike in ammonia and nitrite if you add a medium to heavy load of fish after the initial cycling. Note that some people use flake fish food instead of shrimp but this is not recommended because flake food does not have much organic material compared to shrimp and so does not add a lot of ammonia to the water, but you can use cut fish instead of shrimp. Hint: to speed up the decay of the shrimp/fish and produce more ammonia, add some DrTim’s Aquatics Waste-Away sludge busting bacteria to the tank.
Ammonia toxicity
There are many data on the toxicity of ammonia to fish and shrimp from laboratory tests in which pH and ammonia concentration were constant. The LC50 concentrations (concentrations required to kill 50 percent of test animals) have the following ranges: 0.3 to 0.9 mg/L for coldwater fish; 0.7 to 3.0 mg/L for warmwater fish; 0.6 to 1.7 mg/L for marine fish; and 0.7 to 3.0 mg/L for marine shrimp. Safe concentrations for long-term exposure are around 0.015 to 0.045 for coldwater fish and about 0.05 to 0.15 for warmwater and marine fish and shrimp. In aquaculture systems, pH and temperature vary during the day, and fish and shrimp in culture systems are not exposed to a constant ammonia concentration.
Symptoms include:
Purple, red or bleeding gills
Fish may clamp, may appear darker in color
Red streaking on the fins or body
Fish may gasp for air at the surface of the tank water
Torn & jagged fins
Fish may appear weak and lay at the bottom of the tank
Of all the water quality parameters that affect fish, ammonia is the most important after oxygen, especially in intensive systems. Ammonia causes stress and damages gills and other tissues, even in small amounts. Fish exposed to low levels of ammonia over time are more susceptible to bacterial infections, have poor growth, and will not tolerate routine handling as well as they otherwise would. Ammonia is a killer when present in higher concentrations, and many unexplained production losses have likely been caused by ammonia.
The Nitrogen Cycle
A biological process called the nitrogen cycle eliminates ammonia from the water by converting it to other, less toxic compounds (Figure 1). The ammonia fish excrete is converted to a compound called nitrite (NO2-) by several genera of bacteria, including Nitrosospira and Nitrosomonas. Other groups of bacteria, including Nitrospira and Nitrobacter, convert nitrite to nitrate (NO3-).
Nitrate, the end product of the nitrogen cycle, is considered to be harmless to fish in natural systems and ponds as it is used as a fertilizer by plants, including phytoplankton. In closed systems with little or no water exchange, however, nitrate will accumulate and may be harmful if higher than 250 mg/L.