Introduction to Marine Fish
Monitoring and adjusting
Although the upkeep of a marine aquarium—especially a reef tank—is more demanding than a freshwater system, a few routine maintenance tasks and the judicious use of test kits to check water quality will ensure a healthy environment for the tank occupants. Watch for signs of algal overgrowth, and carefully observe the fish, since abnormal behavior may be an early indicator of deteriorating conditions.
Algae are key ingredients of reef aquariums, but if they become rampant, they look unsightly and may smother corals, causing them to die. While you can physically remove the algal overgrowth, you should also address the underlying cause of the problem, which could be excessive or inadequate lighting, or high levels of nitrate and phosphate.
Monitor pH closely, and regularly check the water’s buffering capacity—its ability to resist a change in its pH. Buffering depends largely on the concentration of carbonate in the tank water, which neutralizes any acidifying substances present.
The calcareous substrate bolsters buffering because it contains calcium carbonate, which gradually dissolves and replenishes the water’s carbonate content. The typical pH range is 8.0–8.3, but pH inevitably falls as carbonate is used up. A carbonate hardness test (also called an alkalinity test) measures the level of carbonate in milliequivalents per liter (meq/l). If the result is outside of the range of 3.0–3.5 meq/l, take remedial action; partial changes of gravel and water help to restore the buffering capacity, as does the addition of a commercial buffering solution.
In an established tank with good filtration, there should be no ammonia or nitrite. The nitrite level increases slightly if you add new fish or invertebrates, reflecting extra waste output, but it soon falls as the nitrogen cycle converts nitrite into nitrate. Use partial water changes to reduce nitrate levels— which should be close to zero and never above 20 milligrams per liter (mg/l)—preferably in conjunction with a protein skimmer (see p.211) to remove waste before it decomposes.
You should also test the concentrations of trace elements, especially in a reef tank. Calcium, strontium, iron, and iodine are vital for a healthy reef community. The ideal levels are 400–475 mg/l for calcium, 8 mg/l for strontium, 0.05 mg/l for iron, and 0.5 mg/l for iodine. You can correct these levels by adding commercial aquarium preparations. Phosphate, too, is essential, but if it exceeds 0.01 mg/l, it can lead to a proliferation of unwanted hair algae (Derbesia sp.).
An excellent way of monitoring the general health of the tank is to install a redox meter, which measures the water’s oxidationreduction potential—that is, the ease with which chemical reactions occur in the water. The reading, in millivolts (mV), should ideally lie within the range of 320–380 mV, indicating that the nitrogen cycle is working well, the water is relatively pure, and oxygenation is good. The redox potential naturally fluctuates over any 24-hour period, due to the biological processes taking place in the tank, so take readings at the same time each day. A sharp decline may signify that the airstone is blocked. Live rock and some types of algae help to raise the redox potential; however, if the redox figure exceeds 400 mV, which can happen if your ozonizer (see p.211) is too large for the aquarium, there may be fatalities among the tank occupants.
REGULAR MAINTENANCE TASKS
- Feed the aquarium occupants in the morning and evening, as required, taking care not to overfeed them.
- Watch the fish feed, because a loss of appetite may be a sign of illness or declining water conditions.
- Check the water temperature, as shown by the thermometer. Any fluctuation suggests a heater malfunction.
- Be sure that you actually see the fish every day. A sudden, undetected death will have a serious impact on water quality.
- Carry out water tests, recording the results to create an ongoing record of the conditions in the tank.
- Add buffering solutions and calcium or trace element supplements as required, based on the results of the water tests.
- Top off the aquarium with dechlorinated tap water, to replace evaporative loss.
- Clean the sides of the tank to remove any algal growth, using a magnetic or longhandled cleaner.
- Carry out a partial water change of about 20 percent of the aquarium volume, using a gravel cleaner to remove mulm from the substrate at the same time.
- Keep an eye on the specific gravity reading and other test parameters. Review figures recorded previously.
- Service filters, rinsing sponge components in water siphoned from the tank. Clean the protein skimmer, and make sure that airstones are not blocked.
- Adjust the level of lighting if algal growth is starting to get out of control.
CHANGING THE WATER
Partial water changes not only reduce harmful accumulations of nitrate, phosphate, and other chemicals by dilution but also replenish levels of carbonate (reinforcing the buffering capacity) and trace elements, which are vital to the well-being of the tank occupants. When setting up the aquarium, make an inconspicuous mark on the side of the tank with a felt-tip pen to show the water level when the tank is full. This makes it easier to fill up the tank with the correct amount of water, both when making partial water changes and when replacing evaporated water.
- Check the salinity and temperature: A conductivity meter gives readings in millisiemens per centimeter (mS/cm). At 77°F (25°C), 50.1 mS/cm corresponds to an SG reading on a hydrometer of 1.023.
- Drain the water and clean the gravel: Fix a gravel cleaner to the siphon and suck up mulm from the substrate while draining the water. This will prevent the undergravel filter from becoming clogged with waste.
- Add more water: Replace the drained water with a fresh, dechlorinated salt solution of the correct temperature and salinity. Test the water for toxic copper before adding it to the tank.
- Clean out the protein skimmer: Carefully remove the accumulated debris from the cup. Then rinse the cup with warm, dechlorinated water to remove fat deposits, which make the skimmer less efficient.
The correct salinity, in terms of specific gravity (SG), will be in the range of SG 1.020–1.025, depending on the species in your tank. Salinity can be tested with a hydrometer or a conductivity meter, which determines the water’s salt content from its ability to conduct electricity. With a hydrometer, you may need to adjust the reading to take account of the water temperature: cold water is denser than warm water, so it gives a slightly lower SG reading. The instructions provided with the hydrometer should enable you to make the right adjustments.
TESTING THE WATER
Tank samples can be tested with reagents to monitor a range of water parameters, including pH and levels of chemicals such as iron, nitrate, phosphate, carbonate, calcium, strontium, iodine, and copper. Read the instructions on the kits carefully, store them appropriately, and use them before they are out of date; otherwise, they will give inaccurate readings that may endanger the health of both fish and invertebrates. Electronic meters give more accurate results for many of these parameters, but they are far more expensive.
NEW TANK SYNDROME
Ammonia and nitrite can rise to dangerous levels in a new tank, before the colonies of beneficial bacteria that break down these toxic waste products have developed in the biological filter. Use test kits to take weekly readings of ammonia and nitrite in a new tank to monitor the progress of this maturation process. Some hardy species, notably damselfish, can be introduced at this time, but most marine species should be added to the aquarium only when the system has stabilized.
- Try not to be away when a tank is in the early stages of maturing or immediately after adding new occupants to an existing setup.
- Carry out a partial water change a few days before you leave, to ensure all is well.
- Leave very clear feeding instructions, in writing.
- Be sure to leave sufficient food and a replacement lighting tube or bulb.