Sense and purpose of floor heating in the aquarium
The task of a floor heater is not to heat the aquarium. A rod heater is used for this. The underfloor heating is intended to create a water flow in the floor. Whether underfloor heating makes sense or not can only be clarified in connection with the question of a suitable substrate.
Thesis 1: Sand without floor heating
Plants need nutrients, some of which they absorb through their roots. Nutrients remain readily available in an anaerobic, ie low-oxygen soil climate. In addition, rot cannot occur in this soil climate because no biological waste or mulm can seep in.
Such an anaerobic soil climate occurs in sandy soil from a depth of about 3 centimeters without the need for soil heating. Fine gravel under 2 millimeters is also suitable, because even in this fine gravel hardly any muck can penetrate. Such a climate does not occur in coarser gravel. Biological waste seeps into gravel, forming rotting spots in the soil. In order to break down these rotting spots, the gravel has to be flushed with water. This water movement is generated by underfloor heating. The underfloor heating therefore only alleviates the problems caused by an incorrect substrate.
Aquariums with gravel, underfloor heating and quick filters only work because the gravel with underfloor heating replaces the quick filter. The biological filtering that should actually take place in the filter takes place in the gravel. This system is very prone to failure. Even a powerful suction of the muck can lead to problems. Therefore, sand can only be used as substrate if the quick filter is replaced by a slower filter, e.g. B. the Hamburg mat filter is replaced.
Thesis 2: Gravel with strong underfloor heating
Anaerobic zones in the substrate not only make nutrients available for plants, but also phosphate. Anaerobic zones do not develop so easily in a gravel soil if the layer of sludge is regularly rejuvenated. Phosphate stays there in the ground. Strong floor heating ensures that the floor remains aerobic.
Plants do not grow well in every aquarium with sand or better than in other aquariums. There are even more problems with sandy soil and plants than with gravel soil with plants, soil fertilizer and soil heating. The cause is not the filter performance. Otherwise aquariums with gravel and floor heating could not work. On the other hand, sparsely populated aquariums with too small a filter and sand should never cause problems. But rot can also occur there. When planting new plants, etc., biodegradable substances get into the substrate, even if the soil is sandy.
If strong underfloor heating is used, the gravel size should be 2 to 5 millimeters. A strong floor heater should have 0.5 to 1 watt per 10 liters of water.
Thesis 3: Gravel with weak underfloor heating
With strong underfloor heating, the substrate becomes too warm. The flow through the substrate is too strong. As a result, the substrate has an aerobic, oxidizing rather than an anaerobic, plant-friendly climate. If the soil is significantly warmer than the open water, some plants will respond by slowing down rather than improving. This is probably due to the fact that the desired anaerobic climate is not created because the soil is perfused too quickly.
The floor heating should only generate a very weak flow in the substrate. This turns the soil into a large, reducing filter.
Therefore, only weak floor heating should be used. At the same time, fine gravel about 1 to 2 millimeters in size is used. Hardly any muck can penetrate the ground. Due to the constant, slow circulation of the water in the substrate, nutrients are constantly carried into the soil. The water around the roots does not run out of nutrients as quickly. Due to this slow circulation of the water, the substrate forms a large anoxic filter. An anaerobic climate develops in the soil, in which there are nutrients for the plants. Anoxic conditions and thus a negative redox value are desirable in the soil. It is only when the redox value falls too far, below -300 mV, that rot can set in in the soil, during which hydrogen sulphide is formed. However, the redox value is stabilized above this limit because some oxygen is constantly getting into the soil.
A weak underfloor heating should have about 5 watts per 100 liters of water.
Thesis 4: Floor heating is not necessary
Some aquarists report that underfloor heating improves plant growth. Other experiences show no significant difference between aquariums with and without floor heating. Even in coarser gravel without underfloor heating, rot does not necessarily have to occur. Even if no muck is sucked off.
In a 240 liter aquarium that was cleared out after 12 years, there was hardly any mulm in the substrate. No rot occurred during the entire service life. The plants grew very well. The aquarium was initially operated with a 75 watt floor heater. In recent years, the heating was in the floor, but was not in operation. The aquarium had an internal filter with foam.
Floor heating with 24 V and 230 V
Floor heaters with 24 V and 230 V are commercially available. For safety reasons, heaters with low voltage numbers are recommended. The additional transformer means that the costs are higher. In the event of a defect, e.g. B. with a damaged insulation, but then there is no danger to life and limb.
However, no concrete cases are known in which people were injured by defective floor heating.
At 230 V, however, currents of just a few mA can be deadly. An RCD reduces the risk of electric shock. FI switches can also be purchased as a version for socket strips if there is no FI switch in the house installation. Even in modern buildings, RCDs are often only used as standard for wet rooms such as bathrooms and showers.
Ideally, the circuit breaker is combined with grounding of the water. A piece of stainless steel is hung in the water and connected to earth. Titanium is best used for seawater instead of stainless steel, e.g. B. Bicycle spokes made of titanium. A ground should never be used without an RCD.
The switch then triggers as soon as the incorrect voltage occurs and not just when someone puts their hands in the pool.
At 24 volts, no dangerous current can flow through the human body due to the human internal resistance. Due to the internal resistance of the human body, the flow below 50 volts is never more than 40 mA. A 12 volt car battery can briefly z. B. deliver over 200 amperes when starting. But only to a consumer that is low-impedance enough. A person, on the other hand, can safely touch the poles of the 12 volt battery due to their internal resistance.
From a current of 40 mA, the human nervous system is severely disturbed. The muscles contract. On the one hand, this is dangerous for the heart, on the other hand, the whole body cramps and you may not be able to get away from the voltage source.
However, high voltage alone does not bother people. Even an ungrounded high-voltage power line could be touched. As with birds, nothing happens. The relevant current flow according to Ohm’s law I = U / R, current = voltage / resistance is decisive.
Voltages up to a maximum of 48 volts are therefore considered harmless to humans. Compliance with this regulation is intended to ensure that the current of 60 mA, which is regarded as life-threatening, does not flow.
Floor heating should only have a low output per meter. 6 to 8 watts per meter are sufficient. A sensibly designed underfloor heating does not have to be regulated if the output is a maximum of 1 watt per 10 liters of water. The constant switching on and off does more harm than good. If necessary, a heating element switches on or off with its normal built-in control.
If necessary, a high-power heating cable can be connected to a lower-power transformer, e.g. B. to a halogen transformer. The performance of the cable is then z. B. back to 1/4 if the transformer is only correspondingly powerful, e.g. B with a heating cable with a 200 watt heating cable on a 50 watt halogen transformer.
Gutter heaters can be purchased from roofers and gutter fitters. These should prevent the downpipes from freezing over. These heaters are available in a wide variety of lengths and outputs. For safety reasons, they are operated with 24 V. Together with a transformer, e.g. B. from Conrad, you get a functioning and safe floor heating. The insulation is relatively thick and chemically stable due to the acid rain and temperature fluctuations, making these heaters well suited for aquariums.
Thermal floor in the aquarium
Advantages of aquariums with a thermal bottom
Disadvantages of aquariums with a thermal bottom
- Natural bodies of water are not heated from below.
- There is a risk that heat will accumulate and the floor will become too warm.
- Floor washers only work optimally if they are in operation as continuously as possible. A thermal floor as the sole, thermostat-controlled heating with high heat output does not work continuously.
- Due to the direct operation on the light network, a considerable potential is evoked in the aquarium by influence. When you reach into the aquarium, a clearly tangible current flows over you.
- In the event of a defect, the aquarium must be disassembled.
To control the temperature, some manufacturers offer appropriate control units:
There are also instructions on the Internet for self-construction of such switches, e.g. B. with the temperature switching module from Conrad Electronic.
A drop in temperature at night can also be achieved with simple means. The temperature that is desired during the night is set on a control heater. The temperature desired for the day is set on a second adjustable heater. The adjustable heater for the day is simply switched off with the lighting or with a separate timer at night.
The control heaters must have the power required in each case.
Temperature values of 30° C when using underfloor heating are often mentioned in discussions. Specific measurements in a 200 x 50 x 50 cm aquarium with 50 watt floor heating and a well-drained gravel floor resulted in the following temperature distribution:
The differences at the same depth were no more than 0.2°C.
The heater was evenly laid in a zigzag pattern at a height of 1 cm above the floor pane in the manure sand. The heating was always active, from about 25.5°C a thermostat switched off.
Especially in the summer months, the water temperature can get too high if underfloor heating is constantly in operation. An inexpensive option is to regulate the underfloor heating with a timer. How long the heating has to be on or off has to be tried out. On the one hand, the water temperature should not fluctuate too much, on the other hand, the heating should not switch on too often. A typical cycle is e.g. B. one hour on and off.