A 20-gallon nano reef costs roughly four times what a comparable freshwater tank costs and takes about three times the weekly maintenance. That math is not a deterrent — it is the honest baseline. Marine reefkeeping has become much more accessible than ten years ago, but it remains the hardest mainstream hobby in the aquarium world. This guide assumes you have run a freshwater tank for at least a year. If not, run one first.
Why reef is harder than freshwater
- Salinity adds a variable. Specific gravity drifts as water evaporates; you compensate with fresh top-off water.
- Corals demand light, flow, and stable chemistry at levels freshwater fish do not.
- Marine fish are caught wild more often than freshwater, arrive stressed, and need quarantine.
- Equipment costs more. A decent LED, skimmer, return pump, heater, and RODI unit easily reach $1,000 before livestock.
Tank size — bigger is easier
The opposite of freshwater intuition. Larger tanks are more forgiving because temperature, salinity, and chemistry shift slower in more water. Recommended minimums:
- Fish only: 20 gallons
- Soft coral + LPS reef: 30 gallons
- SPS (small polyp stony) reef: 40+ gallons
Nano reefs under 20 gallons are possible but punishing for beginners. We do not recommend starting smaller than 20.
Equipment list
Tank + stand
Glass or acrylic. All-in-one (AIO) tanks like the Innovative Marine, Waterbox, or Red Sea Reefer Nano hide the filtration in the back chamber and reduce build complexity for a first reef.
Lighting
LED with full spectrum for coral growth. Budget around $200-400 for a reasonable nano LED. Brands with track records: AI Prime, Kessil A80/A160, Nicrew (budget), Radion (premium). Skip white/blue “plant lights” — they will not grow most corals.
Flow
Powerhead delivering 20-40x tank volume per hour. Wavemakers (programmable powerheads) help avoid stagnant zones. The AI Nero, Hydor Koralia, and Jebao OW series are popular nano options.
Heater
Standard submersible. Run two smaller heaters instead of one large one — a single stuck-on heater can cook a tank in hours.
Salt mix and salinity refractometer
Reef Crystals, Red Sea, Instant Ocean. Refractometer, not hydrometer — swing-arm hydrometers are wildly inaccurate for marine work. Target specific gravity 1.024-1.026.
RODI water
Tap water contains phosphate, silicate, copper, and other contaminants that feed nuisance algae and harm corals. An RODI unit ($150-250) is non-optional for serious reefkeeping. Alternatively, buy RODI water from a local fish store ($1/gallon typical).
Protein skimmer
Removes dissolved organic compounds before they break down. For tanks 30+ gallons, near-essential. For nanos under 20 gallons, weekly water changes can substitute.
Live rock vs dry rock
Both work. Live rock comes seeded with bacteria, copepods, and the occasional hitchhiker (good and bad). Dry rock is sterile but cheaper and has no risk of introducing pests. For a first reef, we recommend dry rock with a small amount of live rock from a trusted source to seed the bacteria.
Cycling a marine tank
Same nitrogen cycle as freshwater, just slower. 4-8 weeks is normal. Live rock that has been kept wet through transport accelerates the cycle dramatically. Dry rock alone can take 8-12 weeks to fully cycle. Dose ammonia or use bottled bacteria as needed.
First livestock — the hardiness ladder
Add in this order, weeks apart:
- Cleanup crew first — hermit crabs, snails (nassarius, cerith, astrea), one or two emerald crabs
- First fish — clownfish. Aquacultured ocellaris or percula. Two together (always purchased together — they pair).
- Second fish — goby pair (yellow watchman, hi-fin red banded, etc.)
- First corals — soft corals. Zoanthids, mushrooms, GSP, leather corals. Avoid Aiptasia (a pest anemone often hitchhikes in).
- LPS corals next — torch, hammer, frogspawn, duncan
- SPS last, if at all — Acropora, Montipora, Stylophora. Stable chemistry required.
Skip for year one
- Tangs — most need 75-125 gallon minimums
- Anemones — wild-caught, often die in the first 6 months
- Mandarin gobies — eat live copepods only, starve in young tanks
- Most angelfish — nip corals
- Acropora and other SPS — too sensitive to immature water chemistry
Maintenance — weekly minimums
- 10% water change with fresh saltwater
- Glass cleaning (magnet scraper)
- Skimmer cup empty
- Salinity check, temperature check
- Top-off with fresh RODI as water evaporates
Monthly: test alkalinity, calcium, magnesium. Quarterly: filter media replacement, deeper substrate vacuum.
Bottom line
Budget $1,200-1,800 for a fully equipped 30-gallon nano reef before livestock. Plan on 6-8 weeks of cycling and 3-6 months before adding more sensitive corals. If you cannot commit to weekly water changes for the next several years, do not start a reef. If you can, it remains the most beautiful tank you will ever own.