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 fish, 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.
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.
Obtaining Medications
As anyone who has visited an aquarium store knows, there is no shortage of commercial medications available for treating fish disease. However, fish medications sold and used in the aquarium hobby can vary in quality and effectiveness. Medications for the aquarium can be found as dry ingredients (crystals or powders), or in liquid form (solutions). Sometimes, the chemical comes in pre-packaged amounts. One should follow the manufacturer's instructions for treatment, as different manufacturers use different chemicals and concentrations of the active ingredients.
It is advisable to use only those fish medications that list the active ingredients on the label so that you know what you are using. Many popular fish medications sold in pet stores will simply not work when used as directed. The delivered dose of active chemical is often below that recommended in the scientific literature; many don't even state the active ingredients. However, it is NOT a safe practice simply to increase the dose rate, and in fact, such measures can have disastrous results. In addition to this, many aquarium chemicals can cause problems with established biological filtration. Therefore, you need to be well informed on the subject of aquarium fish medications and should always seek out the most reliable aquarium specialists when attempting to treat a problem unknown to you.
Medications have an expiration date beyond which they may lose their effectiveness. Light, moisture and elevated temperatures are factors that may dramatically accelerate this rate of degradation. Unfortunately, many remedies available in pet stores do not carry any expiration date, nor are kept under acceptable storage conditions. Warm temperatures, moist environment, or stored on shelving under bright lights are factors that will affect commercial preparations sold in the hobby. Other times it is the hobbyist who decides to use old products! These situations should be avoided.
Unless you have a very large number of aquaria, do not buy medications "just in case". Few treatable conditions require an immediate use of medications, and in most cases it is better to start with water changes or just careful observation; then buy a fresh package of the exact medication that you need. Here are some useful tips to consider on the subject of purchasing and keeping medications:
- Buy medications from a shop that has a high volume of sales and stores them under acceptable conditions.
- Stay away from dusty or moisture-stained packages.
- Sealed containers are preferable to boxes or bottles that can be easily opened and contaminated.
- Formulations with an expiration date and a clear label explaining contents and concentrations are much more reliable than those with unknown or poorly described content.
- Store what you bought in a cool and dry place.
- If you opened an airtight container, it is unlikely that after a few months the content will still be viable, and you should dispose of it in a safe place.
- Keep you aquarium medications out of the reach of other pets or children.
Aquarium Calculations
Chemical treatments can be ineffective if volume is underestimated and potentially lethal if it is overestimated. Before determining the concentration or amount of chemical to be used the water volume must first be calculated. Therefore, all fishkeepers should know the volume of their aquarium or pond.
Exact measurement of volume is essential in order to calculate any chemical applications and should be calculated before a problem occurs. Ponds preferably should be calculated when they are filled with water for the first time. The information is then recorded so it is immediately available when needed. In small ponds, depth should be measured across the pond in at least two directions. The number of different directions that will be needed will depend on the shape and bottom uniformity of the pond and will have to be determined on site. If water depth is not uniform it is important that average depth is measured. Greater number of depth measurements will result in greater accuracy.
Most aquariums used for holding fish are rectangular and the volume of rectangular aquariums is calculated by the formula: Volume (litres) = length × width × depth in centimetres ÷ 1000. When measuring a tank, take inside measurements of length and width and the depth at the appropriate water level. If the bottom of the tank is sloped, an average depth measurement should be used. To get the average depth of the tank, take three measurements: at the shallow end, in the middle and at the deep end. Add these depths together and divide the total by 3.
Circular pond or container volume is determined by the formula: Volume (litres) = 3.14 × radius² × depth in centimetres ÷ 1000. The radius is measured as ½ the inside diameter of the container. The radius is squared or multiplied by itself. For example, a circular container with an inside diameter of 180 cm and depth of 60 cm has a volume of 1526.04 litres (3.14 × 90 × 90 × 60) ÷ 1000.
Aquarium Medication Calculations
All aquarium medications must be applied at a prescribed rate. Accurate application of this prescribed rate is necessary to achieve adequate control of the target organisms, and to avoid unwanted results such as mortality of nontarget organisms. Chemical application rates for aquariums are generally given as a final concentration of active ingredient in the water, usually in parts per million (ppm).
To calculate the dose rate of a chemical required in a given volume of water the formula is:
Dose rate = (required ppm × litres of water to be treated) ÷ percent of active ingredient.
[1 ppm = 1 mg/L; 1 million milligrams = 1 litre; 1000 milligrams = 1 gram; 1000 grams = 1 litre]
The easiest way to find out the total amount of chemical required is to convert the rates into something understandable like milligrams or grams. For example, to calculate the dose rate of 25 ppm (mg/L) of a chemical with an active ingredient of 400 grams/litre in 100 litres of water:
25 ppm x by total litres to be treated = 25 mg × 100 litres = 2500 mg.
2500 mg divided by percent (40%) of active ingredient = 2500 ÷ 0.40 = 6250 mg.
Example:
= (25 ppm × 100 litres) ÷ 40%
= (25 mg × 100 litres) ÷ 40%
= 2500 mg ÷ 0.40
= 6250 mg or 6.25 grams.
© Copyright Adrian R. Tappin
Created July, 2005
Updated December, 2008
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