Water looks the same regardless of what temperature it is, what colorless salts or gases may be dissolved in it, or where it comes from, but chemically it may be very different, and the difference is very important to the fish that must live in any aquarium, including the custom fish tanks.
As an extreme concentration of chlorine is fatal to all fish, the chlorine used in many districts to disinfect the water supply may be a danger. However, the health authorities will not pump water that is too highly chlorinated, and therefore water that is obtained from the faucet will usually be satisfactory in this respect, though even tap water is toxic to some delicate fish. (The more dangerous chloramines are now present in the waters of many cities.) But to be safe, allow the water to stand for a day in the fresh air and in contact with the direct rays of the sun. Before putting it in the tank, scoop out a glassful at a time and pour it back into the container so that the chlorine or other gases dissolved in the water will have another opportunity to escape.
Many aquarists prefer to use pond water, but it has been found that there are many organisms in pond water that are detrimental to the health of certain fish. The safest water for the beginner to use is tap water that has been aerated by the method previously mentioned, or with an air pump, filter, and aerator.
The proper way to introduce this water into the fish tank so as not to disturb the gravel is to place a piece of paper over the gravel and pour the water slowly until the tank is about one-third full. Then take the paper out and anchor the plants in the gravel. Planting is much easier with this method than when the tank is full of water.
Before entering plants of almost all kinds into your tank, however, sterilize them thoroughly in a concentrated solution of salt and potassium permanganate (purple crystals). This will destroy any harmful organisms that might otherwise gain entrance to a healthy tank. Do not keep plants in this solution for more than a few hours or they may be destroyed. When the vegetation is properly anchored, fill the tank up to about one inch from the top, then check again to see if the plants are still firmly in place. Some of the plants are very buoyant and are apt to pull loose from the sand.
Remember an earlier precaution: Before putting any water into the tank, make sure the tank is placed where it is to be located permanently. Water weighs about 8-1/3 pounds per gallon and, besides being quite a load to carry, the sides of the aquarium might be loosened if you move the tank from place to place. Many a time has the bottom fallen out of a large tank when someone tried to lift it off a table. Do not let this happen to you!
Now that the tank is set up and you have all your equipment in place, you are ready for the thermostatically controlled heater. Caution: Be sure to test the heater first in a plain glass container (such as a bottle) with a thermometer to ascertain that the thermostat is set at the desired temperature. if you put it into the tank with fish before checking you may later find that the fish have either boiled or frozen to death.
Before you bring your new fishes home you should have ascertained the temperature at which they were maintained in the tropical fish store. Most dealers keep their aquaria at about 78°F., but this may vary. In any case, 78°F. is a fine temperature with which to start your fish tank. First, then, you must bring your aquarium to that temperature BEFORE any fish are placed in it. This is done by adjusting the thermostat on your heater. There are many ways to do this. One easy way is to put the thermostat into the dealer’s tank and allow him to adjust it to the temperature of that tank. He does this by putting the thermostat into the tank and allowing it about 10 minutes to adjust to the tank’s temperature. Then he turns the adjustment knob on the thermostat until the light just goes on or just goes off, depending upon the initial setting of the thermostat. This setting then is the same as the setting in his tank and is ideal for fish coming from that tank.
Now take the thermostatically controlled heater and place it in your own fish tank. Once it is in place, plug it in and wait to see what happens. In a very short time the light will go on indicating that the heater is working. This means that the water in your tank was colder than the water in the dealer’s tank. It is possible but unlikely that the water in your tank is warmer than that in the dealer’s tank, but should this be the case, then the heater will not go on until the tank cools down. A thermometer will tell you the temperature of your aquarium. A good thermostatically controlled heater will be able to maintain the temperature to within 2° of the control point at all times unless the heat fails in the room and the room temperature is extremely cold.
This is a slightly edited & updated version of an article originally published on “Fish-Aquariums.net”