The nitrogen cycle is the biological process where beneficial bacteria convert toxic ammonia (from fish waste and uneaten food) into nitrite, then into the less harmful nitrate. Before adding any livestock, you must "cycle" your tank — this takes 4–8 weeks. Skipping this step is the most common cause of early fish death.

Live rock is porous rock colonized by beneficial bacteria, microorganisms, and coralline algae. It serves as your primary biological filtration and gives your tank a natural reef look. Most saltwater tanks benefit greatly from it — roughly 1 to 1.5 pounds of quality live rock per gallon is a common guideline.

FOWLR (Fish Only With Live Rock) tanks house fish and live rock with no coral. They're more forgiving of slightly elevated nitrates and don't require as intense lighting. Reef tanks include corals and invertebrates, demanding tighter water parameters, more powerful lighting, and dosing of calcium, alkalinity, and magnesium.

Most reef and FOWLR tanks thrive at a specific gravity of 1.025–1.026, which corresponds to a salinity of roughly 35 ppt (parts per thousand). Use a reliable refractometer rather than a swing-arm hydrometer — the latter is known for inaccurate readings.

The essential parameters are ammonia (0 ppm), nitrite (0 ppm), nitrate (under 10 ppm for reefs, under 40 for FOWLR), pH (8.1–8.3), alkalinity (8–12 dKH), calcium (380–450 ppm), and magnesium (1250–1350 ppm). For corals, also monitor phosphate (under 0.05 ppm).

Tap water contains chlorine, chloramine, heavy metals, and phosphates that can harm marine life and fuel nuisance algae. Most serious hobbyists use RODI (reverse osmosis/deionized) water, which removes nearly all impurities. You can buy RODI water from fish stores or invest in a home RODI unit.

pH typically drops at night when CO2 rises (photosynthesis stops). It can also crash from high CO2 in the room, poor circulation, or insufficient buffering. To raise pH: improve gas exchange by increasing surface agitation, run your skimmer air intake outside the house, or add a refugium with macroalgae on a reverse daylight cycle.

Excellent starter fish include clownfish (hardy and iconic), dottybacks, chromis damselfish, firefish gobies, and royal grammas. Avoid triggers, puffers, and lionfish early on — they are either aggressive, require large tanks, or are difficult to feed. Always research adult size and temperament before purchasing.

Float the sealed bag in your tank for 15 minutes to equalize temperature. Then drip-acclimate by slowly adding small amounts of tank water into the bag over 30–60 minutes. Finally, net the fish into the tank — don't pour the bag water in, as it may contain pathogens or poor-quality water from the store.

Yes — a quarantine tank (QT) is one of the most valuable investments you can make. New fish should spend 4–6 weeks in a bare QT before entering your display tank. This prevents the introduction of ich, velvet, and other diseases that are extremely difficult to treat once in a reef tank with corals and live rock.

Ich cannot be treated in a reef tank with medication. The most effective approach is "tank transfer method" (TTM) or hyposalinity in a separate QT. Remove all fish from the display tank and let it run fallow (fishless) for at least 76 days at 78°F — this breaks the parasite's lifecycle. Copper-based medications work well in a fish-only QT.

A saltwater system typically uses three types of filtration: biological (live rock and biological media), mechanical (filter socks or roller mats to trap particles), and chemical (activated carbon to remove dissolved organics and odors). A quality protein skimmer is also essential — it removes organic waste before it breaks down and pollutes the water. 

For a fish-only or FOWLR tank, standard LED lighting is sufficient. For corals, lighting requirements vary by species: soft corals and LPS can thrive under moderate LEDs, while SPS corals (Acropora, Montipora) demand high-intensity lighting. LED systems with programmable spectrums (blues around 420–460nm) produce the best coral coloration and growth

A protein skimmer uses fine bubbles to pull dissolved organic compounds (DOC) out of the water before they decompose and raise nitrate/phosphate levels. For most saltwater tanks, especially reef tanks, it is considered essential equipment. Size your skimmer for 1.5–2x your tank volume for best results.

A refugium is a separate compartment (usually in the sump) where macroalgae like chaeto (Chaetomorpha) is grown under light. It exports nutrients by physically removing the algae when it becomes dense. It also raises pH, provides a safe habitat for copepods (natural food for many fish), and stabilizes the system overall.

Most hobbyists do a 10–20% water change weekly or biweekly. Regular changes dilute nitrates, replenish trace elements, and stabilize parameters. Use properly mixed saltwater (RODI water + quality salt mix) matched to your tank's temperature and salinity before adding it. Never skip water changes and rely solely on equipment. 

Algae blooms are almost always driven by excess nutrients (nitrate and phosphate) and/or improper lighting. Address the root cause: reduce feeding, increase export (skimmer, water changes, refugium), clean your filter media regularly, and limit light to 8–10 hours daily. Cleanup crew animals — turbo snails, hermit crabs, and sea urchins — also help control nuisance algae.

Remove the fish immediately to prevent ammonia spikes from decomposition. Test your water parameters within a few hours. If ammonia is rising, perform a 20–30% water change. Investigate the cause of death (disease, aggression, starvation, water quality) before adding replacement fish. Sudden unexplained deaths may indicate an undiscovered disease in the tank

These systems replenish calcium and alkalinity consumed by corals. Two-part dosing (separate calcium and alkalinity solutions) is easiest for beginners. Kalkwasser (limewater) is added to top-off water and also raises pH. A calcium reactor uses CO2 to dissolve calcium carbonate media and is best for heavily stocked SPS tanks. Always test before adjusting — over-dosing can crash your tank quickly.