Healthy mandarin
- Rounded, full belly when seen from the side
- Body looks in proportion to the head
- Hops and pecks at rock and sand almost constantly in daylight
- Colours stay bright and the fish is out and about
Free mandarin & copepod calculator
Mandarin Dragonet Readiness & Copepod Calculator
Your tank is usually ready for a mandarin dragonet when it has run for roughly 6-12 months, has plenty of mature live rock and ideally a refugium, few other pod eaters, and pods you can easily see on the glass at night. This free calculator scores your reef on those points, compares pod supply with a mandarin's demand, and builds a copepod seeding and culture plan for the mandarin (Synchiropus splendidus) and the spotted mandarin (S. picturatus).
Readiness calculator
Is my tank ready for a mandarin dragonet?
Fill in your tank. Everything runs in your browser and is saved on this device only.
Readiness
85/ 100Ready
Your setup matches what many reefers look for before adding a mandarin. Keep seeding pods and check a night count before buying.
95 gal (360 L) total water
What moved the score
- +10Refugium with macroalgaeA refugium is a predator-free nursery that keeps sending pods into the display.
- +10Captive-bred or eats frozen foodTaking frozen food takes pressure off the pod population, though the fish still grazes pods all day.
Pod supply vs demand
Supply looks ahead of demand
Pod supply (rough)1.43 mandarin-units
Pod demand1.00 mandarin-units
A mandarin grazes almost all day; its intake is commonly described as hundreds to a few thousand small crustaceans a day. As an illustration only, that is roughly 300-3,000 pods a day for one fish. Demand counts each mandarin as 1 unit and adds part of a unit for every other pod eater. Supply is a rough guess from how much rock has matured (about 60 lb of fully mature live rock per unit), plus the refugium and pod hotel. It is a comparison, not a pod census.
Rules of thumb, not science: 70+ is ready, 45-69 borderline. The score treats a tank as young under about 6 months, looks for roughly 1 lb of mature live rock per gallon, and 30-75+ gal for a wild-caught fish (20-40+ gal if captive-bred and frozen-trained). Reef sources disagree, and no score can guarantee a mandarin will thrive.
Copepod seeding plan
Your copepod seeding plan
Starting bottles
2
Seed before the fish
2-4 weeks
Reseed
Every 3-4 weeks for the first 2-3 months, then as needed based on your night count.
Bottle count is a starting estimate for typical retail bottles; follow the supplier's bottle-per-gallon guidance.
Which copepods to add
A mixed bottle with Tisbe and Tigriopus for the rock and sand, plus Apocyclops for the water column.
Tisbe Tisbe biminiensis
Harpacticoid · Recommended
Benthic: lives on rock, sand and glass
Lives where a mandarin hunts, breeds readily in reef tanks and settles into rockwork and refugiums.
Tigriopus Tigriopus californicus
Harpacticoid · Recommended
Benthic: rock, sand, refugium
Larger and very hardy, so it copes with a wide range of conditions and makes a bigger bite for the fish.
Apocyclops Apocyclops panamensis
Cyclopoid · Recommended
Swims in the water column and settles on surfaces
Fast-breeding cyclopoid that spreads through the tank and refugium and adds variety to the mix.
Parvocalanus Parvocalanus crassirostris
Calanoid · Optional
Free-swimming in open water
Optional: a tiny calanoid used mostly for feeding larval fish. It does little for a mandarin grazing the rock.
Step by step
- Start seeding 2-4 weeks before the mandarin goes in.
- Begin with about 2 bottles of live copepods. This is a starting estimate; follow the supplier's bottle-per-gallon guidance.
- Float the bottle for temperature, then add pods at night with the pumps off, pouring slowly near the rockwork and into the refugium.
- Wait 15-30 minutes before turning the pumps back on so pods can settle into the rock. Leave the skimmer off for that time too.
- Put at least part of every bottle into the refugium, where no fish can eat them.
- Feed live or bottled phytoplankton (Nannochloropsis, Tetraselmis, Isochrysis) to keep pods breeding. Dose per the product label.
- Reseed: Every 3-4 weeks for the first 2-3 months, then as needed based on your night count.
- Do a night flashlight pod count before adding the fish, and again every week or two afterwards.
Night flashlight pod count
Are there enough pods for a mandarin?
A couple of hours after lights out, shine a flashlight on a patch of glass or rock about 10 x 10 cm (4 x 4 in) and count the tiny white pods you can see moving.
Pick what you saw, or enter a count, to check.
Rules of thumb, not science: under 10 pods on the patch counts as a few, 10-49 as dozens, 50+ as swarms. Check several spots; one count is a snapshot, the trend over weeks matters more.
Copepod culture planner
Grow your own copepods in a 2-liter bottle
A home culture is a cheap way to keep reseeding. Keep at least two bottles going on staggered schedules so one crash never leaves you without pods.
Setup checklist
- Clean a 2-liter bottle (or a few) with fresh water only; no soap.
- Fill with clean saltwater mixed to the same salinity as your tank.
- Run airline tubing to the bottom with a slow bubble, no airstone, so pods are not battered.
- Add phytoplankton until the water is lightly green.
- Add a starter culture of live copepods.
- Keep at room temperature, out of direct sun, with the cap loosely on.
- Feed phytoplankton again whenever the water clears, usually every 1-3 days.
Feed phytoplankton per the product label. Start harvesting only once the culture is dense with visible pods.
Week-by-week schedule
Week 1
- Set up bottle A and add the starter culture.
- Feed phytoplankton whenever the water turns clear.
Week 2
- Feed phytoplankton whenever the water turns clear.
- Check with a flashlight: you should see pods moving.
Week 3
- Set up bottle B from part of bottle A, so you always have a backup.
- Feed phytoplankton whenever the water turns clear.
- Let bottle A build density; do not harvest yet.
Week 4
- Feed phytoplankton whenever the water turns clear.
- Harvest about a quarter to a third of the dense bottle through a fine mesh or plankton sieve, and add the pods to the tank at night.
- Top the bottle back up with fresh saltwater and phytoplankton.
- Stagger harvests so the two bottles are never both freshly harvested.
Week 5
- Feed phytoplankton whenever the water turns clear.
- Harvest about a quarter to a third of the dense bottle through a fine mesh or plankton sieve, and add the pods to the tank at night.
- Top the bottle back up with fresh saltwater and phytoplankton.
Week 6
- Feed phytoplankton whenever the water turns clear.
- Harvest about a quarter to a third of the dense bottle through a fine mesh or plankton sieve, and add the pods to the tank at night.
- Top the bottle back up with fresh saltwater and phytoplankton.
- Restart the oldest bottle with fresh water and a scoop of pods if it smells bad or has crashed.
- Stagger harvests so the two bottles are never both freshly harvested.
Week 7
- Feed phytoplankton whenever the water turns clear.
- Harvest about a quarter to a third of the dense bottle through a fine mesh or plankton sieve, and add the pods to the tank at night.
- Top the bottle back up with fresh saltwater and phytoplankton.
Week 8
- Feed phytoplankton whenever the water turns clear.
- Harvest about a quarter to a third of the dense bottle through a fine mesh or plankton sieve, and add the pods to the tank at night.
- Top the bottle back up with fresh saltwater and phytoplankton.
- Stagger harvests so the two bottles are never both freshly harvested.
Log every copepod and phytoplankton dose, night pod counts and your mandarin's health alongside your water tests in My Reef Log.Start tracking free
Body condition guide: is my mandarin starving?
A mandarin can look fine for weeks while it slowly eats a tank's pods down. Check its belly from the side every few days; catching a thin fish early gives you time to reseed pods, train it onto frozen food or move it.
Early signs of starving
- Pinched or sunken belly behind the pectoral fins
- Thin “knife-edge” profile seen from above or from the side
- Head starts to look too large for the body
- Stops hunting, hovers in one spot or hides more
How many copepods does a mandarin dragonet need?
A mandarin is a constant grazer that picks tiny crustaceans off rock and sand from morning to lights out. Its daily intake is commonly described as hundreds to a few thousand pods, so the tank has to keep producing them, not just hold a starting batch.
That is why mature live rock and a fish-free refugium matter more than any single bottle of copepods. Use the night count above as your real-world check.
Can a mandarin dragonet eat frozen food?
Often, yes, if it is captive-bred: many captive-bred mandarins are sold already eating frozen foods such as mysis or enriched brine shrimp. Some wild-caught fish can be trained, usually by offering small amounts in a feeding dish or near the rock where they hunt.
Ask the store to show you the fish eating before you buy. Even a frozen-trained mandarin keeps grazing pods, so it still needs a healthy population.
Male vs female mandarin
Males have an elongated first dorsal spine that stands up like a sail; females have a shorter one. Males are often a little larger.
Never keep two males together: they usually fight. A male-female pair is often fine in a large, mature tank with plenty of pods, but it doubles the food demand.
How to get a reef tank ready for a mandarin dragonet
Step 1
Let the tank mature
Give the reef time to settle. Common advice is roughly 6-12 months before adding a mandarin, longer with dry rock.
Step 2
Add live rock and a refugium
Aim for plenty of mature live rock, often around 1 lb per gallon, and a fish-free refugium with macroalgae as a pod nursery.
Step 3
Seed copepods weeks ahead
Add a mix of Tisbe, Tigriopus and Apocyclops at night with the pumps off, near the rock and in the refugium, several weeks before the fish.
Step 4
Feed phytoplankton
Dose live or bottled phytoplankton such as Nannochloropsis, Tetraselmis or Isochrysis per the product label to keep pods breeding.
Step 5
Check a night pod count
A couple of hours after lights out, count pods on a 10 x 10 cm (4 x 4 in) patch of glass or rock with a flashlight.
Step 6
Add the fish
When pods are easy to see and the score is ready, add one mandarin (ideally captive-bred and eating frozen food) and watch its belly.
Good to know
- Every threshold here is a hobbyist rule of thumb, not science. Reef sources disagree on tank size and age, and no score guarantees a mandarin will thrive.
- Follow the copepod supplier's bottle-per-gallon guidance and dose phytoplankton per the product label.
- Mandarins have a thick slime coat that is often said to make them fairly resistant to ich, but they are not immune; quarantine is still worth planning.
- This tool is educational and does not replace advice from your local fish store or an experienced reefer who can see your tank.
Mandarin dragonet & copepod FAQ
How big a tank does a mandarin dragonet need?
There is no single number. Common advice is a mature tank of roughly 6-12 months and often 30-75+ gallons of total water for a wild-caught mandarin, with plenty of live rock and ideally a refugium. Captive-bred, frozen-trained mandarins lower the bar but still need a steady pod population. Tank age and pods matter more than glass size.
How many copepods does a mandarin dragonet need?
A mandarin grazes almost all day, and its daily intake is commonly described as hundreds to a few thousand small crustaceans. Rather than counting, check that pods are easy to see on the glass and rock with a flashlight after lights out, and that the fish keeps a rounded belly.
Can a mandarin dragonet eat frozen food?
Some can. Captive-bred mandarins are often already trained to eat frozen foods such as mysis or enriched brine shrimp, and some wild-caught fish learn with patience. Even frozen-trained mandarins keep grazing pods all day, so they still need a healthy copepod population.
How often should I add copepods to my reef tank?
Seed several weeks before adding a mandarin, then reseed every 2-4 weeks for the first few months. After that, add more when your night flashlight pod count drops. Feeding phytoplankton per the product label helps pods keep breeding between doses.
Can I keep two mandarin dragonets together?
Not two males: they usually fight. A male-female pair is often kept in a large, mature tank with plenty of pods, but it doubles food demand. Males have an elongated first dorsal spine; females have a shorter one.
Related tools
Fish Stocking Calculator
Check the bioload of your whole fish list before adding a mandarin.
Fish Compatibility Checker
See which tankmates get along, including wrasses and gobies that eat pods.
Quarantine Tank Planner
Set up a quarantine tank for your new mandarin, with pods to keep it fed.
Acclimation Drip Rate Calculator
Drip-acclimate a new mandarin dragonet gently.
Reef Hitchhiker Identifier
Tell copepods and amphipods from the bugs you do not want.
Goby & Pistol Shrimp Guide
Check which gobies compete with a mandarin for pods.
Aquarium Volume Calculator
Work out your display and sump volume for the readiness score.
Reef Dosing Calculator
Plan alkalinity, calcium and magnesium dosing for the rest of the reef.
Planning a mandarin? Log pod dosing, night counts and fish health in My Reef Log.