Setup path, stage 9
First fish for a reef tank: what to add and how fast
Add hardy, peaceful fish a few at a time, with a fortnight between each group, and let the bacteria catch up. Speed is the most common way to undo the patience of the cycle.
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What do you need for this stage?
- Your stocking plan, with adult sizes
- A drip line or jug for acclimatisation
- Food the fish already eat (ask the shop)
- Nitrate and phosphate test kits
Which fish are best for a first reef tank?
Charterhouse suggests the ocellaris clownfish, royal gramma, firefish and Banggai cardinal. Our fish pages mark these and other forgiving fish as good first fish, with the minimum tank size for each:
- Ocellaris clownfish
- Royal gramma
- Firefish
- Banggai cardinal
- Yellow watchman goby
- Tailspot blenny
- Orchid dottyback
Browse all fish filtered to beginner fish. Avoid tangs, angelfish and anything with "not for beginners" on its page until the tank is a year old.
How fast can I add fish?
Dr Tim's (BRS) says no more than two or three fish at a time, with at least two weeks between additions. The BRS 5 Minute Guide is stricter at the start: one fish at a time, two weeks apart; after two or three have settled, several small fish can go in together, and large fish should go in alone.
Order matters more than speed for peace. Add the smallest and most peaceful first and the territorial ones last, so newcomers are not walking into an established territory.
There is no reliable stocking formula. The old "inch per gallon" rule comes from freshwater and ignores body bulk, swimming space and territory. Plan by adult size, temperament and the minimum tank size on each fish page, or try the stocking planner.
How do I acclimatise a new fish?
BRS suggests floating the bag for 15 to 25 minutes to match temperature. Drip acclimatisation is mainly for fish that have been shipped; for fish from a local shop, keep it under 30 minutes and only if salinity or pH differ. Rinse the fish in clean salt water for 30 to 60 seconds as it leaves quarantine, and keep the bag water out of the tank. In an established tank, an acclimation box lets residents see the newcomer before they can reach it.
What are the steps, in order?
- Write the stocking list in order, peaceful first.
- Quarantine the first one to three fish.
- Acclimatise and add them; feed lightly.
- Test ammonia, nitrite, nitrate and phosphate over the next week.
- Wait at least two weeks; check everyone is eating.
- Repeat with the next group.
Your checklist
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What test must pass before moving on?
Before each new group of fish:
- Ammonia and nitrite zero, 24 hours after the last feed.
- Nitrate and phosphate steady for two weeks (not climbing week on week).
- Every fish already in the tank is eating and not hiding.
What are the common mistakes?
- Buying the whole stocking list in one trip.
- Adding the bossiest fish first.
- Feeding heavily in the first week.
- Planning by "inch per gallon".
- Two fish of the same shape and colour in a small tank.
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| How many at a time |
| One or two to start, then small groups, always two weeks apart. |
| Clownfish early or late |
| Early for ocellaris and percula; later for the larger, bolder clownfish such as the [maroon clownfish](/fish/maroon-clownfish/). |
| How many fish |
| No formula is reliable. Use adult size, temperament and tank length. |
Sources
Figures from sources read as a search summary only are shown as typical figures: check them before you rely on them. Found a mistake? Tell us how to fix it.