Plan ahead
Reef tank pests and hitchhikers: friend or foe?
New rock and corals bring life with them. Most of it is harmless or useful. A few pests can wipe out a type of coral. This page helps you tell them apart, and says what each kind of coral dip can and cannot do.
Last checked . How we check
Which hitchhikers are usually harmless?
- Copepods and other tiny crustaceans on the glass: food for mandarins and many small fish (our reading).
- Most bristleworms: scavengers that eat leftovers. A sudden boom usually means too much food (our reading). An arrow crab eats them, but also eats small fish (Practical Fishkeeping).
- Small snails and limpets that arrive on rock: most graze film algae (our reading).
- Asterina starfish: mostly eat film algae, but some forms eat corals, especially zoanthids, so keep an eye on them (Reef Builders, search summary).
Which pests should I remove?
| Pest | Found on | Signs | What to do |
|---|---|---|---|
| Aiptasia (glass anemone) | Rock and frag plugs | Small brown anemones that multiply and sting corals. Regrow from fragments. | Inspect rock and plugs; remove plugs on new frags where practical (BRS). Berghia nudibranchs eat only aiptasia; peppermint shrimp sometimes do (Practical Fishkeeping). |
| Acropora-eating flatworm (AEFW) | Acropora | Brown oval worms, bite marks, egg clusters at the tissue edge or on bare skeleton (Reef Builders). | Dip, scrape the eggs off, and re-dip on the egg cycle. See the timing below. |
| Montipora-eating nudibranch | Montipora | Adults hide on the underside; tissue disappears in patches (Reef Builders). | Some dips killed adults in about five minutes in one club thread (search summary). No dip kills the eggs: remove them by hand and re-dip. |
| Red bugs | Acropora | Tiny red or yellow dots on branches; poor polyp extension. | Keepers treat a separate tank with a prescription-only veterinary wormer that also kills crabs and copepods (search summary). Ask a vet. |
| Zoa nudibranchs, zoa spiders and zoa pox | Zoanthids | Polyps closing or vanishing; small sea spiders; white spots on stalks (search summary). | Pick eggs and spiders off by hand with tweezers; dip. Wear gloves and eye protection. |
| Euphyllia flatworms | Torch, hammer and frogspawn | Flatworms hiding at the base of the skeleton (search summary). | Dip and inspect the skeleton base. |
| Hitchhiking crabs | Ocean-farmed Acropora | Small crabs among the branches (Reef Builders, search summary). | Remove them before the coral goes into the display. |
How do I time treatments for Acropora flatworms?
A 2019 study in Frontiers in Marine Science measured how temperature changes the flatworm’s life cycle:
- Eggs took about 26 days to hatch at 21 C, 15 at 24 C, 11 at 27 C and 9 at 30 C.
- New worms matured in about 32 to 56 days.
- Re-treat after the eggs hatch and before the new worms mature, about 13 to 31 days after the first treatment at 28 C.
- Hatchlings live up to 9 days without coral, so keep treated corals out of the display between treatments.
- A tank with no Acropora for about 21 days at 30 C, or 25 days at 24 C, starves them out.
What does each coral dip kill?
The one point every source agrees on: no dip reliably kills eggs. A dip lowers the risk; it does not remove it.
| Kind | Main target | Notes |
|---|---|---|
| Broad-spectrum pest dips | Flatworms, nudibranchs, small crustaceans, some bacteria | Mix fresh for each batch, dip outside the tank, rinse, never dose into the display, not for invertebrates (BRS). Forums dispute how well some remove pests. |
| Iodine-based dips | Disinfection after fragging or damage; bacterial problems | Gentler. Use a product with a label rather than mixing your own, because home doses vary widely (our reading). |
| Hydrogen peroxide | Algae on frag plugs | BRS mentions it without a dose; treat the plug, not the coral (our reading). |
| Garden insecticides | Arthropods and soft-bodied pests | BRS calls the US product toxic and without aquarium instructions. Not sold for this use in the UK. We do not recommend it. |
| Veterinary drugs | Red bugs, flatworms, nudibranchs | Prescription only, used in a separate tank, and they kill crabs, hermits and copepods (search summary). Ask a vet. |
Can I buy these dips in the UK?
Most US guides name products by brand. Several European brands of coral dip are sold by UK shops; we name none here because we have not compared them ourselves. Read the label for what it targets and how long to dip, and never use a product made for another purpose. See the UK guide for prescription medicines.
Sources
- Bulk Reef Supply, Best coral dips of 2019
- Bulk Reef Supply (Marine Depot archive), Coral RX and quarantine
- Bulk Reef Supply, Pest and parasite control buyer’s guide
- Reef Builders, What are Acropora-eating flatworms and how to treat them
- Frontiers in Marine Science, Acropora-eating flatworm life cycle and temperature (2019)
- Reef Builders, Montipora-eating nudibranch finally has a name
- Reefs.com, Pest-free reefkeeping part II
- Reefs.com, Acropora red bug treatment
- Nano-Reef forum, Common zoa pests, diseases and treatments
- Reef Builders, Remember to de-crab new cultured Acropora
- Top Shelf Aquatics, Berghia nudibranchs guide
- Practical Fishkeeping, Essential cleaners for the reef tank
- Reef Builders, Asterina starfish: an introduction
- PLoS ONE, Palytoxin in Palythoa sold in the aquarium trade (2011)
- US CDC, MMWR: suspected palytoxin inhalation exposures, Alaska 2012 to 2014
- Practical Fishkeeping, Aquarium coral lands fishkeeper and family in hospital