Fishkeeping Guide

Chapter 1

Freshwater or saltwater

This is the first decision because it changes almost everything else: the gear, the cost, the fish and how much work the tank takes. Most people should start with freshwater. It costs less, is more forgiving of mistakes and teaches you the basics you'll need for a reef later.

If a reef is your goal, a year with a freshwater tank is still useful practice. If you go straight to saltwater, read Saltwater basics before you buy anything.

Chapter 2

Choosing a tank

Bigger tanks are easier, not harder. More water dilutes waste and slows down temperature and chemistry swings, so mistakes do less damage. A 20 to 40 gallon tank is a strong first choice. Very small tanks (under 10 gallons) leave little room for error.

Shape matters

Fish use the floor space, so a long, low tank holds more fish comfortably than a tall one of the same volume. A "20 long" (30 × 12 × 12 in) is a classic starter for that reason.

Where it goes

• A filled tank weighs roughly 10 lb per gallon or more. Use a stand built for aquariums, on a level floor.
• Keep it out of direct sunlight, which feeds algae, and away from heaters, vents and doors.
• Put it near an outlet, and somewhere you can reach easily with a bucket.

Chapter 3

Equipment

A freshwater tank needs only a handful of things to run well. Saltwater adds more, covered in its own chapter.

• Filter. It houses the bacteria that break down waste. Aim for one rated to turn the tank's volume over about 4 to 6 times an hour.
• Heater. Most tropical fish want 74 to 80°F. A rough rule is 3 to 5 watts per gallon. Use an adjustable one.
• Thermometer. Don't trust the heater's dial alone.
• Light on a timer. 6 to 8 hours a day to start. Too much light is the most common cause of algae.
• Water conditioner. Removes chlorine and chloramine from tap water. Every bit of new water needs it.
• Liquid test kit. For ammonia, nitrite, nitrate and pH. Liquid kits are more accurate than strips.
• Substrate, a gravel vacuum and a bucket used only for the tank.

Chapter 4

Setting up

1. Wipe the tank with plain water. Never use soap or household cleaners on anything that goes in the tank.
2. Rinse the substrate until the water runs mostly clear, then spread it 1.5 to 2 inches deep (deeper for planted tanks).
3. Place rocks and wood. Build them so they can't topple when fish dig or you vacuum.
4. Put a plate on the substrate and pour water onto it so the substrate doesn't churn up. Add water conditioner.
5. Install the filter and heater. Let the heater sit in the water for 15 to 30 minutes before you plug it in.
6. Add plants, set the light timer, and start the filter.

Your tank looks ready now, but it isn't safe for fish yet. That's the next chapter.

Chapter 5

Cycling the tank

Fish produce ammonia, which is toxic even in small amounts. In an established tank, bacteria in the filter turn ammonia into nitrite (also toxic), and other bacteria turn nitrite into nitrate, which is far less harmful and is removed by water changes. A new tank has none of those bacteria. Growing them is called cycling.

Fishless cycling, step by step

1. Add an ammonia source: bottled aquarium ammonia dosed to about 2 ppm, or a pinch of fish food every day.
2. Test every few days. Ammonia will start falling and nitrite will rise, usually in the first 1 to 2 weeks.
3. Keep feeding the bacteria ammonia. Later, nitrite falls and nitrate appears.
4. The tank is cycled when it can turn a full dose of ammonia into 0 ammonia and 0 nitrite within 24 hours.
5. Do a large water change to bring nitrate down, then add your first fish.

Bottled bacteria products can speed this up, but keep testing. The test results are what tell you it's done, not the calendar.

Chapter 6

Choosing fish

Pick fish that fit the tank as adults, need the same water conditions, and get along. Old rules like "one inch of fish per gallon" don't account for body shape, activity or waste, so check each species instead.

• Adult size and minimum tank. Many fish sold small grow large. Plan for the adult.
• Temperature and pH ranges that overlap for every fish in the tank.
• Temperament. Avoid mixing fin-nippers with slow, long-finned fish, or putting small fish in with anything big enough to eat them.
• Group size. Schooling fish like tetras and rasboras need groups of 6 or more to feel safe and act natural.
• Swimming level. Mixing top, middle and bottom dwellers uses the space well.

Start with hardy, beginner-level species, then work up to more sensitive fish once you have some experience.

Chapter 7

Adding fish

The bacteria colony only grows as fast as the waste load does, so add fish in small batches: a few at a time, with about 2 weeks between batches. Test ammonia and nitrite a few days after each one.

Acclimating new fish

1. Dim the tank light. Float the sealed bag for 15 to 20 minutes so the temperatures match.
2. Open the bag and add a small cup of tank water every 5 minutes for 15 to 30 minutes. Shrimp and sensitive fish do better with a slow drip over an hour.
3. Net the fish into the tank. Throw away the store water rather than pouring it in.
4. Leave the lights off for a few hours and skip feeding until the next day.

A separate quarantine tank for 2 to 4 weeks is the best way to keep disease out of your main tank. It's worth setting up once you have fish you'd hate to lose.

Chapter 8

Feeding

Overfeeding causes more problems than underfeeding. Uneaten food rots into ammonia and fuels algae.

• Feed once or twice a day, only as much as the fish finish in about 2 minutes.
• Use a quality flake or pellet as the staple, and add frozen or live foods a few times a week for variety.
• Bottom feeders need sinking food. Don't count on them living off leftovers.
• Healthy adult fish handle a day without food fine, so a weekend away doesn't need a vacation feeder.

Chapter 9

Maintenance

A small routine done every week beats a big cleanup done when things look bad.

Weekly

• Change 20 to 30% of the water. Match the temperature, and treat the new water with conditioner before it goes in.
• Vacuum the substrate as you drain, to pull out waste.
• Wipe algae off the glass, and check that the heater and filter are running.
• Test the water weekly for the first few months, then every couple of weeks once things are stable.

Monthly

• Rinse filter sponges in old tank water you've removed, never under tap water. Chlorine kills the bacteria.
• Never replace all the filter media at once. Swap parts in stages so the bacteria survive.
• Trim plants and clean the lid and light.

Chapter 10

Water quality

You can't see most water problems until the fish react to them, so testing is how you see them early.

Stability matters more than perfection. Fish handle a steady value at the edge of their range better than one that keeps jumping around.

Chapter 11

Troubleshooting

When something looks wrong, test the water first. Most problems trace back to it.

Chapter 12

Saltwater basics

Everything above still applies. Saltwater adds a few rules of its own.

• Use purified water. RO/DI water keeps out the phosphate, silicate and metals in tap water that feed algae and harm corals.
• Measure salinity with a refractometer. Aim for a specific gravity of 1.025 to 1.026. Swing-arm hydrometers drift and aren't reliable.
• Top off with fresh water. Only water evaporates, and the salt stays behind. Topping off with saltwater raises salinity. An auto top-off makes this easy.
• Flow matters. Powerheads keep water moving over rock and corals.
• Live rock is the filter. Most of the bacteria live in the rock. Many reef tanks also run a protein skimmer.
• Go slow. Saltwater cycles often take longer, and corals do best in a tank that has run stably for several months.