One of the most essential aspects of supporting a healthy ecosystem for the crayfish is to maintain optimum water quality. High levels of ammonia, nitrite, and nitrate are toxic for aquatic organisms. Also, extremely low levels of dissolved oxygen and high levels of carbon dioxide in the water will cause suffocation. The pH and alkalinity are also key factors to monitor. A few simple tests can be performed to ensure that the quality of water in the tank is adequate to promote crayfish survival. The procedures for all of the tests recommended on this site are listed here. The tests are designed to give you the ability to understand the cycles in your tank and how they effect the ecosystem. Through the data you collect, you will make changes in your tank, helping create a better ecosystem. Feel free to do any other tests besides these, these are just some important and interesting ones.
This test measures the amount of oxygen that is dissolved in the tank’s water. Crayfish require a dissolved oxygen level of at least 3 ppm or they will die or be injured. The ideal environment for crayfish is saturated with oxygen , so a good dissolved oxygen level is around 9 ppm. A low DO level could be caused by the lack of oxygen producing plants or heavy pollution that removes the oxygen from the water.
The test is performed with the use of a dissolved oxygen meter, which can be purchased from equipment dealers such as Omega and Eutech Scientific, Inc.
A high carbon dioxide level means the dissolved oxygen level is low, so typically a lower carbon dioxide measurement is preferred. The carbon dioxide level can go as high as 50 mg/mL and still have surviving crayfish, although the higher the level of carbon dioxide the less oxygen there is for the crayfish and this can hurt the crayfish.
This test can be performed by using water quality testing strips sold by many major scientific equipment catalogs such as Hach or a spectrophotometer. Make sure to follow the instructions carefully and record your results.
Ammonia is the most toxic form of aquatic nitrogen, it can poison the crayfish at relatively low concentrations . At 1 mg/L it begins to cause damage to the system and optimum levels are under 0.5 mg/L.
All of the gasses in the tank (Oxygen, Nitrogen, Carbon Dioxide etc;) effect the acidity of the water, the pH. For instance a high carbon dioxide measurement would indicate that there is a high pH. A pH higher or lower then the normal 6.5-9 can injure the crayfish and the plants in the tank.
Measure using an aquarium thermometer that can remain in the water and use consistent units. The ideal temperature for crayfish growth is around 22 C. Crayfish thrive in warmer temperatures, but their metabolism becomes more active then, increasing their waste production and decreasing the oxygen-carrying capacity of the water.
General observations about the behavior and appearance of the organisms should be made daily as well. For example, if the plants are turning brown this might indicate a oxygen/ carbon dioxide imbalance. Crayfish migrating to the top of the water may indicate low levels of oxygen in the tanks.
Nitrite and Nitrate
Like ammonia, these tests can be performed by a spectrophotometer or by water quality testing strips (sold by or any major scientific equipment catalog).
Nitrogen is found in the two forms of nitrite and nitrate (and ammonia). Nitrogen is broken up by bacteria in the nitrogen cycle to form these chemicals. They are not as toxic as ammonia and therefore only need to be monitored every three days.
Nitrite is less toxic then ammonia is and it should not exceed 4 mg/l.
Nitrate is much less toxic then ammonia or nitrite but it can build up in a system if the water is not changed periodically. Nitrate levels from 60 mg/L are considered fair for aquatic systems and the less nitrates the more excellent the water (Morgan, 1989).
Maintaining a standard water level in your tank during the project is important. If the water level is rapidly decreasing, a major problem could be evident in your tank. Check for any leaks in the tank and make sure it does not go so low that the crayfish have little or no water above their heads. A greater amount of water is a good buffer against wastes overwhelming the system as there is more water for the substance to be spread out in. However too much water does not leave any room for trapping oxygen that can be incorperated into the water and if the water level is too high a crayfish might escape.
The change in alkalinity is more gradual and therefore only needs to be checked 2-3 days a week. Alkalinity is the systems ability to resist changes in pH which would disrupt the system, so a high alkalinity concentration is desired.
Record the milliliters of sulfuric acid required - each milliliter of sulfuric acid is equal to 10 mg/L CaCO3 in the sample water
Water that has become thick with sediment is turbid. In the tank this is caused by the excretion of waste and the growth of microbes in the water. It increases slowly, but can cause blockage of light in the tank, causing plants to die, taking away a food and an oxygen source for the crayfish. Turbidity also indicates other problems in the water such as high concentrations of organic matter that consume oxygen..
A spectrophotometer can be used to perform this test.
Testing the mass of the crayfish gives you many insights into the amount of food and oxygen they need/have. Other factors like molting, fighting(loss of limbs), growth and reproduction also contribute to the biomass of the crayfish.
Lots of plants are needed to sustain the eating and breathing of the crayfish. If the biomass is decreasing, the crayfish are eating the plants faster then they can grow. To correct this problem at the sealing period, add more plants.
As with any design, certain unexpected problems may occur that warrant necessary emergency action. If one or more of the following events occur, any member of the group has the right to break the seal on the tank and rectify the situation:
If any other unexpected situation presents itself, the group will discuss the options available to address the problem. Run tests on the tank to try and pinpoint the problem.
While fixing the tank be sure to place your crayfish in a safe place and feed them food pellets until they are ready to be returned to the system.