which can travel out into the main system and kill fish. Once the water flows out of the contact chamber, it should be passed through either a biological filter, and/or activated carbon, UV, or intense heat to remove residuals; these may be known as ozone destruct units. Packed column aeration is another technique for removing residuals from the water, particularly trihalomethanes. In this process, the water is trickled down a tower filled with inert material as a fan blows air upward into the tower. Most residuals are volatile and are released into the air. Ozone is short‐lived, so many residuals can also be limited by simply increasing contact time in the contact chamber. Residuals can also be reduced by creating salt mixes that are low in bromides.
Ozone needs to be carefully monitored to ensure animal and human safety. This may include:
1 Monitoring ozone generation (often 0.3–0.5 mg/h/gallon) or actual ozone dose (often 0.01–0.50 mg/L).
2 Monitoring oxidation‐reduction potential (ORP) in the contact chamber and in the aquarium (Figure A3.15c and d). This is often 700–800 mV for optimum disinfection in ozone contact chambers but should be <200–350 mV in the fish habitat. The trend in aquarium systems is to try to reduce this to avoid dosing above demand.
3 Monitoring residual oxidants, particularly total and free bromine. These should be very low in fish systems (HOBr < 0.02 mg/L).
4 Testing for ambient ozone leaks.
5 Testing turbidity.
6 Monitoring bioload in the system and changes in feeding and cleaning schedules.
7 Monitoring plastic, rubber, and metals as these deteriorate more rapidly in the presence of ozone.
Temperature Control
Temperature is a core factor whose importance is underestimated in the aquarium world. Animals have thermal preference zones and many ectotherms behaviorally regulate their body temperature. Thermal refuges are difficult to achieve in the aquarium setting because of the high thermal conductive nature of water. That being said, this is an ideal that the aquarium professional should strive for as technology evolves.
Currently, water temperature is controlled in bulk using heaters, chillers, heat exchangers, and insulation. Smaller systems may have independent heaters or chillers to sustain water temperatures within the thermal preference range of the species and to limit wide temperature fluctuations. Larger systems typically have heat exchangers (Figure A3.16). Heat exchangers should be placed last in‐line before water returns to the aquarium or pond. Heat exchangers should be sized correctly for the temperature range of the species being maintained, the ambient temperature range, and the size, flow rate, and thermal characteristics of the system. It is important to remember that the heat exchangers themselves generate heat, which can impact aquariums in enclosed spaces. Heat exchangers should be constructed from materials that will not contaminate the system (e.g. heavy metals); titanium heat exchangers are usually the best choice, especially for saltwater aquariums.
Figure A3.15 Ozone disinfection system showing the ozone gas generator (a), ozone injection into the foam fractionator contact chamber (b), and oxidation‐reduction potential (ORP) reading (in mV) from the contact chamber (c) and the aquarium habitat (d).
Source: Images courtesy of Ashleigh Clews, National Aquarium.
Heaters and chillers (as well as pumps) can easily cause electrical issues if not grounded properly. These should be checked immediately if stray current is suspected.
Noise and Vibration
Noise can be an underappreciated stressor for fish and invertebrates in human care, affecting health, growth, and reproductive success (Anderson et al. 2011). Hearing sensitivities vary widely, but tend to be in the lower frequency range, particularly for vibrations intercepted by the lateral line system. Noise and vibrations can be generated from many areas, but common sources are pumps and water running through pipes that come in contact with the sides of the aquarium. Abrupt noises can be an intense source of distress since they are stochastic and unpredictable. Examples include nearby construction or someone tapping the sides of the aquarium. Construction noises from other areas (even across a street) can find their way into a system through acoustical conduits. Animals should be monitored for startle reflexes or repetitive swimming behavior; behaviors such as these should trigger an analysis of the situation. Large aquariums or culture facilities might consider investing in hydrophone monitoring equipment.
Figure A3.16 Heat exchanger.
Source: Image courtesy of Catherine Hadfield, Seattle Aquarium.
There are many ways to minimize noise and vibration. Pumps may be mounted on rubber bushings (Figure A3.17). Pipes resting against systems can be lifted using neoprene or closed‐cell foam to limit sound transfer. Background natural sounds can be used to mask unexpected noises.
Lighting
Light intensity, spectrum, and photoperiod are important parts of the life support system. Lighting impacts feeding, reproduction, and behavior. A review of 38 species of Hawaiian fish demonstrated the great variety of visual sensitivities. Spectrums varied between 347–376 nm (ultraviolet) and 439–498 nm (blue light) and vision was affected by the lenses, corneas, and humors (Losey et al. 2003). It is important to understand the spectral needs of the fish species being housed to maximize welfare. Excess light intensity can lead to sunburn and cataracts. Scala et al. (2016) found retinal neoplasms in hybrid striped bass (Morone saxatilis) and pajama cardinalfish (Sphaeramia nematoptera) housed in systems with high‐energy blue light produced by metal halide lamps. And some fish show bioluminescence or phosphorescence that is strongly impacted by lighting. Not only does one have to consider animal welfare, but lighting also has aesthetic effects that are particularly important in display aquariums.
Figure A3.17 Rubber bushings for mounting of pumps to minimize noise and vibration.
Water filters the light spectrum, absorbing red light within the first few centimeters. The aquarium professional tries to recreate natural environments through manipulation of lighting, e.g. high intensity for shallow tropical reefs, blue for deep‐water habitats, or infrared for complete darkness. With mixed species habitats, it is hard to target lighting to each species.
The need for full spectrum lighting for fish has been a topic of debate. In particular, the need for UVB remains controversial. UVB penetration depth is mainly influenced by water turbidity and the number of photons contacting the water. In the ocean, only ~10% of surface UVB can penetrate down to 35 m at full sunlight with minimal total organic carbon in the water (Aas and Højerslev 1999). A major challenge for large aquariums is the permeation of light using artificial bulbs. Bulbs have a high energy output and lose light intensity with distance due to the inverse square law of light (light intensity is inversely proportional to the square of