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Fish Care (Part 2 of 2)

Water conditions play a key role in the health and happiness of your fish. In our previous article, we introduced some key factors in aquarium keeping. We reviewed the roles of nitrates and ammonia in the aquatic environment, as well as the chemical components, often undesirable, of municipal water, and how to adapt your aquarium to be a most accommodating environment. This article will address a few other factors in aquarium keeping: pH, hardness, temperature, and the buildup of organic pollutants. These, coupled with regulation of ammonia and nitrate, and removal of chemical treatments previously discussed, amount to an ideal environment for pet fish which must be maintained to achieve stability.

Water hardness is the concentration of metal ions in the water (known as cations: calcium, magnesium, iron, and zinc). Hardness can be split into permanent and temporary hardness as it pertains to the anions. Temporary hardness is also known as alkalinity and is the measurable carbonate in the water. The temporary hardness is also defined as the water’s buffering capacity. Temporary hardness can be removed if the water is boiled. The permanent hardness is comprised of the nitrates, sulfates, and chlorides that are not removed by boiling water. In the fish tank environment, we can think of hardness as mainly the products of calcium and magnesium ions in the water. Buffering is a product of bicarbonate and carbonate ions. As a rule of thumb, hard water is usually well-buffered and soft water is usually less well-buffered. Buffering stabilizes pH by mopping up extra hydrogen ions. Knowing the kind of fish you have is important because some fish like soft water (e.g. Amazon rainforest fish) and others like hard water (e.g. African cichlids). It is important that the hardness of the water be stable for the kind of fish you are keeping, most pet stores sell water hardness kits so you can monitor the hardness of your fishes’ water. Products are sold to help maintain optimum water hardness if necessary.

The pH of the water your fish is living in related to the hardness and is also very important for your fishes’ health. The pH measures free hydrogen ions in the water. It is measured on a 1-10 logarithmic scale, with 1 being a strong acid (battery acid), and 10 being a strong base (sodium hydroxide). Most fish live in a pH range of 7.5 to 8.5, but the habitable range varies between species. Many things influence pH in the fish tank, such as photosynthesis, respiration, and nitrification. Abnormally high or low pH levels can cause direct physical damage to the fishes’ gills, skin, and eyes. Prolonged exposure to sub-lethal pH levels can cause stress to the fish and make them predisposed to getting disease and dying. The pH level will also influence disease treatments, making some compounds more or less effective. For example, high pH will make ammonia more toxic. It is important to measure both pH and water hardness and maintain the levels in the optimal zone for the kind of fish you are keeping.

Water temperature is very important for fish physiology. The temperature will influence the amount of dissolved oxygen in the water and the microorganisms in the fish food chain. Water temperature also directly impacts the fishes’ ability to fight disease, heal wounds, and digest their food. For fish living outside, they are very vulnerable in the springtime as they are still sluggish, so it is common to see infections and parasites at this time. It is important that tropical species be kept in their optimal temperature range, usually between 72 and 80 degrees Fahrenheit. Temperature is also an influence the amount of dissolved oxygen in the water; as temperature goes up dissolved oxygen goes down, and as temperature goes down, dissolved oxygen goes up. Keeping fish at the optimal temperature for their species is ideal.

Another key water parameter is the level of dissolved pollutants. These are other non-nitrogen fish metabolites that build up in aquaria, such as fish waste, uneaten food, and algae. Biological filtration will take care of ammonia and its byproducts, but there will be a buildup of organic and inorganic compounds as dissolved chemicals and particulates. The best way to manage these compounds is to make sure your filter is rated for the size of your tank and make sure to do frequent water changes.

Understanding the first four water parameters: Low ammonia and nitrite; chemically clean water; water hardness, pH and temperature; and low levels of organic pollutants, leads us to the fifth parameter – stability! It is important that fish tanks and ponds be maintained at stable levels. Many fluctuations in the temperature, salinity, hardness or pH, even if they are in the normal range for that species of fish, can be very stressful and cause the fishes’ immune system to weaken and predispose them to illness. The best way to achieve stability is to measure the parameters discussed above. Ammonia, nitrites, and pH should be tested weekly as maintenance and more frequently if the system has been disturbed or medicated. Nitrates should be tested every month in a freshwater aquarium, and weekly in a marine, coral, or invertebrate tank. Water hardness should be tested monthly. Salinity should be tested in marine tanks at least weekly. Dissolved oxygen should be tested if the temperature is rising in the tank. The temperature should be measured daily. Water changes should be performed at least every 4 weeks in a closed system (fish tank or small pond), more frequently if there is an issue, or higher stocking densities are present. It is also imperative to make sure the new water used is free of chlorine or chloramines.

Keeping fish can be a rewarding experience, but it is by no means an easy task. Understanding these 5 points is essential to their care and will help to become a better fish keeper!


Should you have any questions, comments or concerns, please don't hesitate to contact us by phone at 845-876-6008, or by e-mail at [email protected].

Thank you for choosing us to be part of your pet's healthcare team!

With warmest regards,
Your friends at Rhinebeck Animal Hospital

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