Chemical Treatment
It is important to keep in mind that all fish medications are toxic to fish and treatment should not be undertaken without a thorough understanding of the potential problems that can occur. Fortunately, it usually takes a higher concentration of the drug to harm the fish than it does to harm the pathogens. Nevertheless, subtoxic doses for the fish are still stressing, and repeated doses can build up to toxic levels. The toxicity as well as successful use of chemicals frequently depends on dosage, abiotic parameters (e.g., temperature, hardness, organic load or pH, the species, and the developmental stages of fish.
When using any treatment for the first time, a bioassay (a test to determine safe concentration) should be conducted on a few fish before large numbers of fish are exposed. Over treatment with chemicals can cause serious damage to fish. Fish species can react differently to various concentrations of the chemical; therefore, fish undergoing treatment must be monitored closely for adverse reactions. If the fish react negatively to treatment, the chemical should be flushed immediately from the system, or the fish should be moved to fresh water. However, fish that do not improve as expected should be rechecked and retreated if necessary.
Before applying chemicals double-check the chemical you are using and the concentration to be delivered. Proper calculation of concentration is contingent upon accurate determination of volume of water to be treated. If you are uncertain as to the volume of water to be treated then take the time to measure the size of the aquarium so that volume can be accurately determined.
A popular means of medicating fish is to place a chemical into the water with the fish. However, the addition of chemicals to water containing fish must be done carefully so that the entire chemical is mixed uniformly throughout the water column. If the chemical is not thoroughly mixed, areas of high concentration of chemical may be formed which can damage or kill the fish. To ensure uniform application, chemicals can be pre-dissolved in water prior to application. Aeration can be used to help distribute chemical throughout the water column. If treating in an aquarium with undergravel filtration remove the airstones or powerheads from the uplift stacks and place them in the aquarium proper to prevent the medication from passing through the gravel. Remove any activated carbon from filters but maintain flow for maximum water movement.
Any time a water treatment is utilised, attention must be paid to the concentration of the chemical applied and the duration of exposure to that chemical. There are three basic water treatments: dips (less then 1 minute), short-term (about 1 hour), and prolonged treatment (indefinite). The difference between these treatments is the concentration of the chemical applied and the period the fish are in contact with the chemical. If too little chemical is added the treatment will be ineffective; if too much is added or if the fish are left in contact with the chemical too long, they may become stressed or die.
Antibiotics are drugs that are usually taken internally to control bacterial infections. Therefore, medicated feed or injection, are preferred for treating systemic (internal) bacterial infections. Dose rates are based on fish weight and are expressed as weight of chemical per weight of fish per day for a specified number of days. Improper doses may result in ineffective treatment or mortalities. Water treatment with antibiotics should only be considered when treating primarily external bacterial infections of the skin and gills of fish. However, the effectiveness of antibiotic therapy for aquarium fishes has been inconsistent and, as a consequence, mortalities continue to occur.
Antibiotic efficiency has been declining for various reasons, not least the development of bacterial resistance. Antibiotic susceptibility testing on fish isolates is rarely performed, and resistance appears to be highly dependent on the infecting species and strain. Resistance to commonly used antibiotics is an emerging problem in the ornamental fish industry.
When faced with a tank of sick or dying fish, usually the person is more concerned with how to treat the problem rather than with resolving what is the cause of the problem. A common mistake of many hobbyists is misdiagnosing disease problems and treating their sick fish with the wrong medication or chemical. When the chemical doesn’t work, they will try another, then another. Selecting the wrong treatment because of misdiagnosis may be more detrimental to the fish than no treatment at all. Successful aquarists learn by experience.