This page is about my 55-gallon reef tank, which I started in January 1999 after about four months of reading. I'm not an expert; I'm a careful beginner who writes things down. I kept freshwater fish for years and I had the idea that saltwater was "the same but harder." It isn't the same. It's a small piece of the ocean in your living room and it has its own rules. What follows is what I've learned in nine months, with numbers, because I found when I was starting out that most pages either had no numbers or had numbers that disagreed with each other.

If you're thinking about a reef tank, please read the mistakes section first. I mean it.

• Tank: a standard 55-gallon glass tank (48 inches long) on a wood stand. Bought used with the stand. Check used tanks for scratches and old silicone; I filled mine in the driveway and let it sit for a day before I trusted it.
• Live rock: about 60 pounds. This is the heart of the whole thing. "Live" rock is rock from the ocean covered in bacteria and small critters, and it's your biological filter. Most of my budget went here and I don't regret a dollar of it. Stack it so there are caves and gaps for water to flow through, not a solid wall.
• Sand: a couple of inches of aragonite sand on the bottom.
• Protein skimmer: a hang-on unit that pulls dissolved gunk out of the water as foam before it can break down. It's ugly and it makes a noise and the collection cup fills with something that smells like low tide. It's the second most important piece of equipment.
• Lighting: a power compact fixture, four bulbs, a mix of daylight and blue (actinic) bulbs, on a timer for about 10 hours. Corals are animals that farm algae inside themselves and the algae needs real light. Regular aquarium lights are not enough for a reef.
• Sump: a 10-gallon tank in the stand under the main tank. Water drains down to it through an overflow box, goes through a filter sock, past the heater, and a pump sends it back up. It adds water volume (more stable), hides the heater, and it's where I top off evaporation.
• Powerheads: two small pumps in the tank for water movement. Corals like current.
• Heater: a submersible heater in the sump — and after what happened in June (see mistakes), a second one, set a degree lower, as a backup.
• Test kits: ammonia, nitrite, nitrate, pH, alkalinity, calcium. Plus a hydrometer for salinity and a good thermometer. Not optional.

These are the targets I keep the tank at, and what it tested at on September 23. A reef is more about stability than hitting a perfect number; a tank that swings is worse than a tank that sits a little off.

Two things I didn't understand at first: salt water evaporates as fresh water, so the salt gets more concentrated as the level drops. You top off with plain fresh water (I use water from a reverse-osmosis unit), not salt water, and you only add salt water when you do a water change. And mix new salt water a day ahead in a bucket with a powerhead in it, and match the temperature and salinity before it goes in the tank.

Before any fish can live in a new tank, the bacteria that turn fish waste (ammonia) into less harmful stuff (nitrite, then nitrate) have to grow. That's the "cycle," and with live rock, the rock brings the bacteria with it — but some of the life on the rock dies in shipping, and as it rots, ammonia spikes. You wait it out. Here's how mine went, from my notebook:

• Week 1 (mid-January): Rock in, sand in, water in, lights off. Ammonia went from 0 to high within days. Smelled bad. Skimmer going full blast, cup full of brown every day.
• Week 2: Ammonia still high. Nitrite starting to show. Did nothing. Wanted to do something. Did nothing.
• Week 3: Ammonia dropping. Nitrite high. Brown algae (diatoms) covering everything, which is normal and ugly.
• Week 4: Ammonia near zero. Nitrite peaking. Little white feather-duster worms showing up on the rock. Some tiny snails I didn't buy.
• Week 5: Ammonia zero, nitrite falling fast, nitrate rising. Did a 20% water change.
• Week 6 (late February): Ammonia 0, nitrite 0, nitrate about 15. Tested three days in a row to be sure. Cycle done. Another water change. Lights on.

Six weeks. Some people's tanks go faster. I'd rather wait too long than too short, and after what happened in March (see mistakes), I'd wait even longer.

• A pair of ocellaris clownfish (the orange-and-white ones). Added in March, one at a time a couple of weeks apart. They've paired up, and the larger one is the female; clownfish are all born male and the dominant one becomes female, which is the kind of fact that makes my nephew's whole day. They sleep in the same corner every night. They don't have an anemone and don't need one.
• A cleaner shrimp (the white-striped kind with long antennae). Added in May. It set up shop on a rock and the clownfish visit it to be picked at. It molts about once a month and the first time I found the empty shell I thought it had died.
• Soft corals: a rock of mushroom corals (blue and red, they've spread), a green star polyp colony that's crawling across a rock, some button polyps, and a leather coral that closes up for a day after every water change and then opens bigger than before. All started as small cuttings from other hobbyists' tanks, which is cheaper and better for the reef than wild-collected pieces.
• Snails: about a dozen turbo and astraea snails as the cleanup crew. They eat algae off the glass and rock all day. If one falls on its back it can't always right itself, so I flip them.
• Uninvited: feather dusters, tiny brittle stars, little pods that come out at night. All came in on the rock. All welcome.

That's it. It doesn't sound like much for a 55, and that's on purpose. Reef tanks are lightly stocked. I might add one more small fish this winter. One. After quarantine.

The whole thing is maybe 20 minutes a day and an hour on water-change day. The notebook is the most important tool I own. When something goes wrong, the notebook tells you what changed.

1. I added fish too fast. In March, one week after the cycle finished, I bought the first clownfish, and then five days later I bought a damselfish because the store said they were "hardy," and then four days after that I bought a second clownfish. The bacteria couldn't keep up. Ammonia showed up again, the damsel died within a week, and the two clowns were breathing hard at the surface until three water changes in four days brought it back down. Entirely my fault. One animal at a time, then wait at least two weeks and test before the next one. I've kept to that ever since.
2. The heater failed — stuck ON. June 14. I came home from work and the tank was at 86 degrees and climbing, the leather coral was slumped over, the mushrooms were shriveled, and the shrimp was hiding. I unplugged the heater, floated bags of ice in the sump, and got it back to 78 over about six hours (slowly on purpose; a fast drop is its own shock). I lost one mushroom rock and a piece of the leather. Everything else recovered. Now I have two smaller heaters instead of one big one, so either one alone can't cook the tank, and I check the temperature twice a day. Heaters fail. Plan for it.
3. I didn't quarantine. Related to number 1. I have a 10-gallon quarantine tank now. New arrivals sit in it for three weeks before they go in the display.
4. Tap water. For the first month I topped off with tap water. Hello, algae. Switched to RO water and the algae faded over a couple of months.
5. I put the tank where the afternoon sun hits it. Can't move it now. Curtains.

People ask, and I think they should know before they start. This is nine months in, including the mistakes.

Plus maybe $15 a month in salt, food and electricity. The lights are the electric bill. Not counted: the quarantine tank, the notebook, and my wife's patience.

Other animal people on GeoCities.us: Mr. Whiskers' Cat Emporium · Backyard Birds of Wisconsin · and for the real thing, Our Hawaii Trip, where a family saw more fish snorkeling in a week than I'll ever keep.

Questions, corrections, or your own tank's numbers: [email protected]. I answer everything, eventually. If you disagree with something here and can back it up, I'd like to hear it; I'd rather be corrected than be wrong for another nine months.