Lighting and Heating

Indoor aquaria, not in a special fish room, rarely receive ideal illumination, which is natural daylight coming from directly overhead. If they get sufficient daylight, they usually receive it at an acute angle through a window at one side or at the back. This is satisfactory for most fishes and does not cause too much disturbance to plant growth as long as the tank doesn't get a great preponderance of very oblique light. If it does, the eventual result will be plants all growing at an angle or at least with leaves unevenly developed, and fishes swimming at an angle, particularly the barbs and some of the characins, which seem to be very sensitive to lighting.

Much of this trouble can be rectified by a combination of shading and a mirror, so directed that oblique light is reflected downwards into the tank more or less vertically, as in the figure. Of course, time of day and season of the year will need different adjustments for exact vertical illumination, but a surprising amount can be achieved with a fixed system which is adjusted only every few weeks.

Large tanks can stand quite a bit of direct sunlight, and, if it can be arranged so that this falls more on the back and sides and not much on the front glass, the former will become coated with a lush growth of algae, and the latter can be kept clear with only an occasional wiping with steel wool. The algae will act as automatic light screens and usually provide a very pleasant-looking background to the other plants,giving a look of maturity and depth to the tank, and providing food for the livebearing fishes. Care must be taken to avoid overheating the tank, and it must be recalled that the tank goes on absorbing heat even when the algal coat has formed. A heat-preventing screen must be behind the tank, not against it, and preferably of white, reflecting material on the face towards the sun. A sheet of glass painted white is  usually excellent but may still admit too much light.

Light Needed by Plants

The prime necessity is adequate light for the plants, as quite dull illumination is sufficient for most fishes. Plants, however, function and flourish only in good light, and many of them need bright light for much of the day to grow properly. Light of insufficient intensity for comfortable reading is quite useless for them. The various species of Cryptocoryne and Sagittaria can take less illumination than the rest and should be used whenever there is doubt as to the brightness of the light in the tank. At the other extreme, plants like Caboinba and Myriophyllum grow stringy and drab and die off if not in bright light and become a menace instead of an ornament and a help in the tank. Only actively growing plants, and that means adequately lit plants, are an asset to the aquarium.

The light utilized by plants in photosynthesis is from the red end of the spectrum, and the growing habit of tinting the back and side glasses of tanks blue is to be avoided when oblique natural light of borderline intensity is employed. A significant amount of the useful rays are removed in this manner, but they are  not removed, of course, when the light comes from overhead and not through the glass.

When there is excess light, such as to cause a blanket of green algae over not only the glass but plants and rocks as well, it can always be cut down by shading. This shading is best applied to the windows admitting the light, as heat absorption which is likely to accompany the excessive light is avoided as explained above. If it must be applied to the tank, use white or light surfaces so as to reflect as much heat as possible and not to absorb it.

Winter daylight in most parts of the world is not adequate for indoor tanks and should be supplemented with electric lighting. In tropical tanks, this can often be done by immersing the greater part of the bulb in the water, so as to utilize the heat which is needed at that time of year. After a short time it will be necessary to clean the algae from the bulb, or little light will penetrate. Such a water-cooled bulb is very efficient and has a long life, but care must be taken to see that the bulb is immersed before switching on the current, not afterwards, or it will shatter.

Artificial Light

For all practical purposes, artificial light now means electric light, but it is worth noting that both gaslight and pressure lamps can be successfully adapted for aquarium lighting. Oil lanterns do not give a bright enough light to be practicable.

Artificial light must be bright and close overhead. The light in an ordinary room is quite inadequate, even if the tank sits underneath the source of light, unless this is a veritable beacon. Either ordinary electric light bulbs or fluorescent lighting may be used. Fluorescent lights have the advantage of causing little additional heat when this is not wanted. Whichever be the choice, it is usual to enclose the overhead tank lights in a reflector, which increases the light thrown into the tank and also prevents dazzle. Most reflectors are not usually of a very efficient design, and they also tend to decrease the life of bulbs, which get hotter when hooded over, so that aquarium toplights rather frequently need replacements.

The overhead lighting may be toward the front or back of the tank. Its appearance and the general direction of plant growth will differ in the two circumstances, and it all depends on which you like. The tank with front lighting  ends to have a gloomy back and to give an impression of depth and spaciousness, but the plants at the back may not flourish too well after a period. The tank with back lighting has a fine background growth of plants and looks generally lighter and therefore rather less spacious and intriguing, and the fishes  are transilluminated when they swim to the front. This gives an effect which depends on the fish; some look very pleasant and others lose effectiveness. On the whole, back lighting seems the less popular. A movable top light is the obvious solution.

Lighting Intensity

With ordinary bulbs, whether frosted or plain, and a reflector of average efficiency, the following are the requirements of various tanks, assuming no help from even weak daylight:

Translated into more useful terms, the figures in the last column multiplied by 100 give the wattage to employ, assuming 10 hours per day of illumination. Thus, a 40-watt bulb turned on for 10 hours over a 5-gallon tank is satisfactory, giving 0.4 kilowatt-hour per day.

Those familiar with the inverse square law may start to do a little figuring for themselves and wonder why a 45-gallon tank, with twice the depth of a 5-gallon tank, doesn't need 4 times the wattage instead of a mere 2 1/2 times. There is a twofold reason. First, the difference in plant depth is not doubled because the tank depth is doubled. Plants right down on the sand will be perhaps at about double the distance, but not the average plant leaf, which will often be able to reach just as near the bulb, whatever the tank depth. Second, the use of a reflector modifies the inverse square law and focuses the light into a beam or band projecting it down into the tank and not allowing it to spread out as much as the light from a naked bulb. It also so happens that, even without an overhead reflector, the internal reflection from the inner faces of the glass prevents the escape of much of the light and aids the illumination of the deeper parts of the tank.

The figures recommended are thus a mixture of theory and experi- ment—mostly the latter. Although it would give about the same result to illuminate a 15-gallon tank with 120 watts for 5 hours instead of with 60 watts for 10 hours, it is best to use the weaker light and a longer period, since the fishes do better that way. If, on the other hand, it is desired to illuminate for a longer period, then 40 watts for 15 hours would be quite in order. There has been a lot of controversy about longer periods of illumination, extending even to constant illumination for 4 hours a day, and its effects on fishes, although there can seldom be any reason for wanting to illuminate adult fishes constantly, unless to supply oxygen via the plants in a very crowded tank. Adult fishes definitely rest in the dark, possibly because they can't see to do much else, but they do not sleep. There is no evidence known to the author that constant illumination harms them, apart from hearsay reports.

Fry, on the other hand, are sometimes given prolonged or constant lighting to keep them feeding and growing—which it certainly does, without obvious harm. In a fry-raising tank it would probably be a good idea to run at a higher total kilowatt-hours per day, as the fry are very actively consuming oxygen and producing waste, and the plants need to be in top form. A 30 to 50% increase seems in order.

Fluorescent Lighting

Fluorescent lighting looks very fine over fish tanks, but not all fluorescent tubes are suitable. Some give too much light at the blue end of the spectrum and do not benefit the plants. It is therefore best to use those which copy natural daylight more closely, and this does not mean that so-called "daylight" tubes are the best. In the Mazda series, the "warm white" tubes are better and give more yellow-to-red light than the "daylight" tubes. Reports indicate that if daylight tubes are used they must be switched on for longer periods.

Fluorescent lighting is much more expensive to install but cheaper to run. The cost of replacements plus initial installation probably makes it rather more expensive all told. However, each watt of fluorescent lighting gives a little over 3 times the actual light given by a watt of tungsten filament lighting, so that the figures in the table above should be divided by 3 for fluorescent tubes.

Twin lamp circuits are best because they reduce flicker when alternating current is used. Fluorescent lamps may be used with direct current, but their life is then shorter, and a reversing switch must be included in the circuit so that one end of the tubes does not become dark from metallic deposits. This switch reverses the direction of the current and should be flicked over frequently, say every other day at least. The general fitting should be undertaken by an electrician, unless one of the new screw-in types is used, as they can be placed in an ordinary lamp socket, having all necessary accessories built in.

Since fluorescent lamps operate at only about 100°F., they do not heat the  urface of the water as do filament lamps, which is a great advantage in hot weather. Another advantage is the spread of light  given by the long luorescent tubes, with resultant even illumination and absence of glare.

Heating

As with lighting, electricity is so much more general and satisfactory for heating aquaria than any other method that oil and gas represent nothing more than auxiliary emergency measures. In fish rooms or houses, steam or hot water may, of course, be used. Electric heating has all the advantages—it may be left indefinitely without attention, it is clean, odorless, and usually cheap, and, most important, it does not have to be applied to the bottom of the tank and thus heat the roots of plants.

With electricity, a few simple definitions and formulas are helpful. With either alternating or direct current, the amount of electric en- ergy used by a heater or any other apparatus is measured in watts. One watt is the amount of energy utilized when one ampere flows at a pressure of one volt. A thousand watts, or kilowatts, used for one hour, gives the familiar unit of electricity, the kilowatt-hour. The heating capacity of a heater depends on its consumption of current; the higher the wattage, the more heat produced. Typical heaters are rated at 12 1/2, 25, 37 1/2, 50, 75, 125, 150, 175, 200, and 250 watts, but other series are available at 10, 20, 30, 40, 50, 75, and 100 watts, so that it is possible to obtain a ready-made heater of almost any wattage required. This is important when different tanks are to be heated by separate heaters but all controlled by one thermostat.

The unit of resistance of a conductor is the ohm. It is related to watts, volts, and amperes so that:

The wattage of a heater of 500 ohms resistance when a 110-volt current is passed is therefore (110 X 110)/500 = 24.2 watts Wire for use in heaters is lways rated at a certain number of ohms per foot or per yard, so that the length required in a heater can be calculated if the current and the desired wattage are known.
 
Ohms required = (volts)2 / watts                      

The heat loss from a heated tank depends mainly on the radiating, conducting, and evaporating surfaces of the tank, and on the difference between tank and air temperatures. Other things being equal, a small tank requires more heat per gallon (more watts per gallon) than a large tank, because it loses heat more rapidly. In theory, we should expect the heat loss to be proportional to the surface area and, in similarly shaped tanks, to the square of any one dimension. Since the volume of such tanks is proportional to the cube of any one dimen-
sion, the number of watts per gallon required for a given temperature to be maintained should be inversely proportional to the length or height of the tank. This is roughly borne out in practice and holds over a useful range of tank sizes. The rate of heat loss from similar tanks, other things being equal, is also approximately proportional to the square of the air-water temperature difference. Thus it takes about four times as much heating to keep a 10°F. difference as a 5°F. difference from the tank's surroundings. This is because the greater part of the heat loss does not occur by radiation or simple conduction,
which follow a different law, but by convection and, in uncovered tanks, by evaporation. With low differences in temperature between tanks and their surroundings, the rate of heat loss follows much more nearly a square law than anything else, although this is not the relationship to be expected at greater temperature differences.

These observations may be stated in a few more simple formulas, taking as a standard a covered 15-gallon tank (2-foot tank) kept at 20°F. above room temperature. This tank requires 4 watts per gallon, a total of 60 watts, to keep it at the stated temperature. (Naturally, in actual practice a thermostat would be included to cut off the heat at a certain point to allow for fluctuations in room temperature.)

The watts required per gallon for tanks of the same general shape but of different size, all to be kept at 20°F. above their surroundings, is given by:

Watts per gallon =4Xl15/lx where lm = the length of the 15-gallon tank  (usually 24 inches) lx   = the length of any other tank.

Thus a 3-gallon tank, of 14-inch length, requires not 4 watts per gallon,but 4 X (24/14), or 6.9 watts per gallon, a total of 21 watts approximately for the tank to be held 20°F. above its surroundings.

The watts required per gallon for the same tank, or others nearly identical with it, at different temperatures is given by:

Watts per gallon = 4X- t2 / 202
where t is the temperature difference required.

Thus a 15-gallon tank to be held at 8°F. above its surroundings re- quires 4 X (82/202), or 0.64 watts per gallon, a total of 9.6 watts.

These formulas may be combined, so that the requirements for tanks of similar shape may be predicted. Almost no rectangular tanks likely to be used by the aquarist will differ enough to matter.
Watts per gallon = 4 x(l15/ lx) X (t2/202)
where the symbols have the meaning defined above.

From the above, we may deduce the wattage of heaters required under different conditions, and the relative heater capacities required when one tank acts as a control for the others, some or all of which are of different gallon capacities. The circuits which may be used in such linked tanks are discussed below.

The following table gives the information for a maximum rise of 20°F., i.e. the heaters would be adequate to raise the water in all tanks to 20°F. above air temperature, but not more. The heating capacity needed for greater or lesser differences can be worked out as above. The tanks are assumed to be double cubes—i.e., a 15-gallon tank measures 24 X 12 X 12 inches, covered by a glass sheet. The last column of the table is of particular importance. Being calculated for a 20°F. rise, it covers all normal requirements and is therefore a column of the heater wattages to be recommended for tanks of different sizes. These wattages gave adequate heat but at the same time make it unlikely that the fishes will be cooked, even if the heater remains on when it should be switched off—either through a thermostatic fault or forgetfulness.

It should be noted that these figures are based on the assumption that the tanks are full of water. Planted tanks with sand and an air space will have less water in them, particularly small tanks, and, although the rocks and sand act in part as if they were water, the general effect is a reduction in equivalent water volume. For complete nicety of calculation, therefore, one might consider true water volumes, but this will rarely make as much as 1°F. difference to the result.

Types of Heater

Electric heaters may be of glass or metal exterior, and they may be totally submersible or so constructed that their tops must not be placed under the water. Metal heaters are less fragile than glass ones but are somewhat likely to cause water poisoning unless of first-class manufacture. They cannot be used in marine tanks unless made of stainless steel or other guaranteed brine-resistant metal. It is more usual to have glass heaters, preferably of Pyrex glass.

Internally, the heater is essentially a heating coil, wound on a ceramic or Pyrex glass form. This may be surrounded by a layer of fine sand or left bare, inside the outer tube, which is sealed with a rubber bung or cap through which pass insulated flex wires. Submersible heaters are watertight; others are not, and so must stand vertically in the tanks with their tops out of water. The resistance wire, usually of thin nichrome or similar alloy, heats up as does an electric radiator element, and it is therefore necessary to make sure that the business part of the heater is covered by water, or it will fuse. This wire is usually in the lower half of upright heaters, and tanks should never be allowed to fall  below about two-thirds full in case of heater trouble. For the same reason, care should be taken not to leave heaters on when emptying tanks, or to plug in a dry heater, or, worse still, to plunge it into water if it does get hot. Even Pyrex glass may not stand up to such treatment, and soda glass certainly will not.

Metal heaters should be earthed, and they usually have a special lead for this purpose. Glass heaters cannot be earthed as such, but the tank and the water in it can be earthed by placing an earth wire so that it contacts the metal frame and the water. Do not worry if a small bare copper wire touches the water, for the amount of metal is too small to produce ill effects.

Totally submersible heaters are popular, as they are not conspicuous and also because of the belief that they heat more efficiently. This is not correct; whether the heater stands upright or lies along the sand, it causes a current of hot water to rise to the top of the tank and does not heat the water uniformly. The heater should never be buried in the sand; if it is, it may fuse and it may also kill the neighboring plants.

As an alternative to the use of conventional heaters, rubber-covered cable is available which may be laid along the base of the tank. It was originally designed for hothouse purposes but is quite suitable for the fish tank. There is  no point in using electric heating below the base of tanks, as the great fault of other types of heating, the heating of the sand, then occurs. When hot water or steam pipes are laid below, but not touching, tanks in a fish room, it is fortunate that much of the heating occurs as the hot air circulates up around the back and sides, and the actual floor heating effect is minimal and plant growth is usually satisfactory.
Thermostats

Although a low-wattage heater may in fact be used without any control on its output, it is usual and much safer to include a thermostat in the circuit. The almost universal type in aquaria is the bimetallic strip. This is a strip of two types of metal which expand at different rates with a rise in temperature, causing the strip to bend as the temperature rises. The strip carries the electric current, but at the critical temperature a terminal on the strip breaks contact with a terminal in the instrument and the current ceases to flow. As the tank cools again, contact is once again established. The "differential," as it is called, should not exceed a couple of degrees Fahrenheit—i.e., the thermostat should control the temperature within 2°F.

Various refinements make a good thermostat reliable and noiseless. It should have a magnetic "make," which means that the strip, once it gets near to completing the circuit, is snapped over into position by a small magnet, thus preventing sparking or arcing. The contacts should be of silver to prevent excessive wear, and there should be a condenser or capacitor to prevent radio interference. If it is not built into the instrument, it may be added afterwards quite easily; a suitable condenser is about 0.02 microfarad.

The thermostat is nearly always non-submersible and is clipped onto the side of the tank. It has a glass body, with the works inside it, and a control, which consists usually of a small adjustable screw with a non-conducting portion so that the operator can alter the setting of the bimetallic strip, and hence the temperature of the tank. Often a pilot light is present which indicates when the thermostat is operating. There are more expensive models in which the thermostat proper is outside the tank, and a temperature "feeler" is placed in the tank like a
submersible heater. Some combination models of thermostat-plusheater are also available and seem to be satisfactory. However, they can be used only in a single tank and hence each combination must be repeated for every additional tank.

The wattage of a thermostat is the number of watts it can safely control. A usual figure is 500 watts, but anything between 100 and 2,000 is available. A 500-watt thermostat may be used in conjunction with heaters totaling not more than 500 watts. It will often have a multiple plug, allowing several heaters to be plugged directly into it in parallel. Two 100-watt heaters in parallel will mean a current producing 200 watts through the thermostat, and so on, but it must be noted that two 100-watt heaters in series means only 50 watts through the thermostat, and an output of 25 watts per heater. This is important when using heaters in series, as outlined below.

LIGHTING   AND   HEATING

Are You Ready To Move Onto The Next Lesson? Click Here….