Reef aquarium, a coral reef in the living room.
Living corals, a few small fish and a lot of water testing. Expensive, demanding and hypnotic to watch.
What it is like
A reef tank is a small, closed piece of ocean. Corals are animals that live on light and very clean, very stable water, and keeping them is mostly a matter of keeping the water right: salinity, temperature and a handful of dissolved minerals, tested and logged.
It is the most demanding hobby on this site and one of the most absorbing. The first months are slow on purpose. Tanks that are rushed are the ones that fail.
Indoors · Solo, A club
Is it for you?
You will probably love it if
- You enjoy measuring, logging and adjusting
- You can give it twenty minutes most days and an hour each week
- You are home often enough to notice when something is off
Maybe not, if
- You travel a lot with nobody to check the tank
- The start cost would be a stretch
- You want fish swimming in it next weekend
The starter kit - $673
- All-in-one nano reef tank, about 20 galFiltration and pump built into the back; the simplest first reef$260
- Reef-capable LED lightCorals feed on light; a standard aquarium lamp is not enough$150
- Heater with thermostatReef temperature has to stay steady$32
- Dry rock and sandThe structure and most of the biological filter$110
- Salt mix and a refractometerTo make and measure seawater$61
- Test kits: ammonia, nitrate, alkalinityYou cannot see water quality$60
- Everything you need to beginAbout $50 a month after that$673
Typical US prices for entry-level gear, rounded. Last checked October 2026. How we get the numbers
Your first project: cycling the tank
Rock, sand, mixed saltwater at 35 ppt, heater and pump running.
Add a bottled bacteria starter and an ammonia source, then leave the lights mostly off.
Ammonia rises, then nitrite, then both fall to zero while nitrate appears. This takes four to eight weeks.
A small clean-up crew of snails first, then one hardy fish, then soft corals over the following months.
Water and mains electricity share a small space: use a drip loop on every cable and a GFCI outlet. Some corals, notably zoanthids and palythoas, carry a potent toxin - wear gloves and eye protection when handling or cutting them and never boil or scrub live rock indoors.
The numbers a reef tank is kept at
Common target ranges for a mixed reef. Stability matters more than the exact figure.
| Parameter | Usual range |
|---|---|
| Salinity | 35 ppt (specific gravity about 1.026) |
| Temperature | 76 to 80 F |
| Alkalinity | 8 to 12 dKH |
| Calcium | 380 to 450 ppm |
| Magnesium | 1,250 to 1,350 ppm |
| Ammonia and nitrite | 0 |
Why people quit
- Adding animals too fastMost losses happen in the first three months, in tanks stocked before the cycle finished.
- Chasing numbersSudden corrections do more harm than slightly off readings. Change things slowly.
- The running costSalt, test reagents, electricity and replacements add up. Budget for it before buying the tank.
How it compares
| Reef aquarium | Backyard chickens | Terrariums | Bonsai | |
|---|---|---|---|---|
| Start cost | $673 | $467 | $52 | $76 |
| Each month | $50 | $30 | $2 | $8 |
| Space | A corner of a room | A backyard | A shelf | A balcony or yard |
| Noise | Low | Medium | Quiet | Quiet |
| First result | 2 to 3 months | About 5 months to eggs | 1 afternoon | 1 growing season |
| Mess | Salt water | Bedding and droppings | A little soil | Soil and clippings |