2. Water Quality

Fish consist essentially of water. Before you introduce high quality fish into your pond, and periodically while they live there, you must test the water.

Water should be first of all be free of chlorine, poisons, and heavy metals. If you must use tap water to fill your pond, be sure your local authority treats with chlorine. If they do, then leaving the water out in a plastic bucket or container for a day or two will allow the chlorine to evaporate. Better yet, buy a chlorine filter like Pond Fresh. If the water is treated with chloramine, you will need to buy a water treatment from your pet supplier. Some experts say that adding water totaling 10 percent or less to your pond does not require chlorine elimination, as it is not enough to endanger the fish, but others say that a small amount, while not directly harmful to fish, will retard the growth of good bacteria. Never allow insecticides or commercial plant fertilizer to drift or run into your pond.

Never, ever use a garden hose to draw the water. The chemicals used to maintain the flexibility of those hoses poison animals and can cause illness even in humans. Use only a hose designated safe for drinking water. These are often called camper or marine hoses and are white in color. Some self coiling hoses in standard colors are also designated “drinking water safe” on their packaging.

Do not allow anything metal in the pond. Heavy metals are poisonous to marine life. Some items are manufactured of marine safe aluminum alloys, such as Koi Kastle, and these are okay. The best rule would be to only allow metal in the pond if it is specifically manufactured for pond use. Brass is doubly bad, as both copper and lead are bad news. Ditto with plant pots – only lead free ones should be allowed, and it is best to buy from your pond center, not your local garden center.

Once you have established your filter, you need to test the water to make sure it is “cycling” properly. When fish waste breaks down, lethal ammonia results. One set of beneficial bacteria in the filter (and to a lesser extent the pond) convert the ammonia to nitrites. Nitrites cause irritation of the gills and depress the immune system. Fortunately, when nitrites are present, a second group of bacteria arises which morphs the nitrites into nitrates, which are more or less fertilizer. These two processes are known as “the cycle.” A mature filter and pond will produce low or unmeasurable readings of ammonia and nitrite and a manageable level of nitrates.

Test your water weekly in warm weather, whenever you introduce new fish, and any other time there is an event in your pond. Water quality is more crucial in warm temperatures and high pH situations, as metabolism and chemical reactions are accelerated.

API makes a great test kit with enough basic tests to last a year. Ammonia should be 0. Retest the next day if you find any, and if you get two positive tests, take action with a chemical treatment and then increase filtration and cut feeding. Above .5 you risk fish loss. Nitrites should also be 0, but .25 or less is fine. Above that level, fish will begin to exhibit inflammation of the gills, scratching themselves, gasping, and flashing about. Brown gill disease will result if high concentrations continue, and 5 ppm or more is fatal. Nitrates do not directly harm the fish, but high levels can compromise the immune and reproductive systems and stunt young fish. Keeping nitrates under 20 will help keep algae under control. Generally, the best way to control nitrates is to introduce plants.

If you experience an ammonia or nitrite “spike,” test daily to see whether the filter cycles through it. Many times, the ecosystem gets a bit out of balance and self-corrects. Change up to 20% of the water if levels are dangerously high. If the filter does not begin to drop the levels, there are treatments available to correct the situation. Do not rely on chemicals to keep your pond in balance, however. If water problems continue, you have to adjust the level of filtration, the fish “load,” or their diet.

pH plays a role in water quality as well. Pond fish like a basic pH from 7.4 to 8.6, but very high pH can exacerbate the effects of an ammonia or nitrite, and can shock new arrivals if they come from a tank with a much lower pH. If you have high or unstable pH, perform frequent water changes, test for water hardness, and get advice on how to buffer it based on the hardness, also known as kH.

Oxygen is the last piece in the water quality puzzle. Water must be aerated in a closed pond system during all but the coldest weather, and it doesn’t hurt to do it then as well. A waterfall, fountain, or air stone will do the job, and some filters have a phase where they spray the water to add air. If your fish are gasping or hanging around at the waterfall and your nitrates and ammonia are in line, then you might need more aeration. Oxygenating floating plants like water hyacinth and water lettuce help as well. Remember, plants may add oxygen during the day, but they use it at night, so keep your aeration running 24/7. Generally, plants work like a dream, adding oxygen when the water is warm and its holding capacity is weakest, taking it when the water is cooler and more oxygen rich.

Salt is a matter of much discussion. You must apply a level of .1% (about a tablespoon per gallon) not to pose a threat to plants, and some people say that is not enough to make a difference for the fish. Indeed, most bacteria can tolerate that level, and .3 to .6 is needed to curb them, Salt does, however, mitigate the effects of nitrite spikes, and our local pond guru George insists the fish have more energy in a slightly salted pond. My experience bears that out. That small salt concentration lowers the osmotic pressure (the difference in salinity between the pond and the fish’s own fluid) making it a little easier for the fish to excrete waste via water exchange. Others have found that even a small amount of salt stunts and damages delicate tropical plants without noticeable benefit to the goldfish.

If you add salt, use only pure NaCl without iodine or any flowing or caking agents. This will be labeled as rock salt, sea salt, kosher salt, pond salt, or solar salt.  The cheapest way to buy salt in bulk is solar salt crystals (not pellets) packaged in bulk bags for water softeners. A forty pound bag costs about 5 dollars.

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