Cherry shrimp dying: failed molts, copper, poisons and water changes, and how to stop it

When cherry shrimp die, the cause is almost always the water, not a disease. The big killers are sudden changes (especially large water changes), copper and pesticides (including pet flea treatments and household sprays), ammonia in a new tank, and the wrong hardness, which causes failed molts.

Don't panic and change everything at once. Test the water, think back over what changed in the last few days, and make small, steady corrections.

How to identify it

Failed molt ("white ring of death"): a pale band appears where the head meets the body. The old shell has split all the way round instead of just across the back, and the shrimp gets stuck. Shrimp found dead half out of their old shell, or lying on their side near a shed skin, also point to molting trouble.
Sudden mass death: many shrimp dead within hours, often after something was added or sprayed. Think poison: copper, insecticide, soap, cleaners or air freshener.
Frantic swimming: shrimp darting around the tank, swimming at the surface or trying to climb out. A strong warning of poisoning or a sudden water change.
Slow, steady losses of one shrimp every few days: often unstable parameters, a new tank without enough biofilm, or poor hardness.
Deaths right after a water change: the change was too big, too fast, a different temperature or hardness, or not dechlorinated.
Milky-white body (not the ring): possible muscular necrosis, an untreatable disease. Remove the shrimp.

Finding an empty, intact shell is good news: shrimp shed their skin regularly as they grow. Don't remove it straight away; they eat it to recover minerals.

When it's a problem

Normal: an occasional death in a large, breeding colony. Cherry shrimp live about one to two years.
Early: two or three deaths in a week, or a single white ring.
Serious: several deaths a week, several shrimp with white rings, or no babies surviving.
Emergency: many shrimp dying within a day, or shrimp swimming frantically. Act now.

What to do right now

Stop adding anything. No fertiliser, medicine, plant treatments or new products.
Test ammonia, nitrite, nitrate, pH, GH and KH, and copper if you have a test. Ammonia and nitrite must be zero (see ammonia).
Think back 48 hours. Did anyone spray fly or bug spray, air freshener or cleaner near the tank? Apply a flea treatment to a pet, then touch the tank? Add new plants, decor, or fish medicine?
If poisoning is likely: do a 30–50% water change with dechlorinated water carefully matched in temperature, add fresh activated carbon to the filter, and repeat the next day. In this case speed matters more than matching hardness perfectly.
If poisoning is unlikely: don't do a big water change. Small changes (10%) with well-matched water, added slowly, are safer.
Remove dead shrimp if you don't know why they died, so they don't foul the water.

What to do next

Copper

Copper is deadly to shrimp and snails at levels fish barely notice. It comes from copper-based fish medicines and algaecides, some plant fertilisers, corroding copper pipes (run the tap for a minute before collecting water), and decor with metal parts. If copper is present, run fresh carbon or a metal-removing resin and do repeated water changes. See copper.

Insecticides and flea treatments

Many modern insecticides are extremely toxic to crustaceans. Fipronil, an ingredient in some pet spot-on flea treatments and household pest products, killed about two-thirds of young brown shrimp (a marine species) in a lab study at just 0.1 micrograms per litre, a tiny trace. Imidacloprid, another common flea and garden insecticide, slowed their growth and molting. Dwarf freshwater shrimp haven't been tested as closely, but there's no reason to think they're tougher. Wash your hands well after touching a treated pet, never spray insecticides in the fish room, and be wary of new plants that may have been sprayed at the nursery. Buy "invertebrate-safe" or tissue-culture plants, or rinse and soak new plants for several days.

Hardness and molting

GH too low (soft water): shells stay thin and soft and shrimp can't build a new one properly. Raise GH slowly with a remineralising product, a piece of cuttlebone or a little crushed coral.
GH too high: shells get thick and hard, and shrimp struggle to break out. Lower it slowly by mixing in some RO or distilled water (see water types).
Cherry shrimp generally do well around GH 6–10 (4–10 is tolerated), KH 2–5, pH 6.8–7.8 and 20–25°C (68–77°F). Stability matters more than the exact number.
Change hardness gradually over weeks. Shrimp need time to rebuild minerals in their bodies.

Water changes

Freshly molted shrimp absorb water, so a big swing in hardness or temperature can shock them. Change about 10% a week, or 20% every two weeks, with water matched to the tank, and add it slowly (dripping it in through airline tubing is ideal). Always use dechlorinator.

New tanks

Tanks under about two months old often have small ammonia spikes and too little biofilm, the film of microbes shrimp graze on all day. Make sure the tank is fully cycled (see cycling), add shrimp in small numbers, and add leaf litter or a piece of seasoned wood for them to graze.

Cautions

Fish medicines: most are risky for shrimp. Treat fish in a separate tank.
Feeding: feed only what the shrimp clear in a couple of hours. Overfeeding brings ammonia and planaria.
Pests: hydra can catch baby shrimp; many hydra treatments also kill snails.

Products that help

Liquid test kit including GH and KH: the most useful tool for shrimp keepers.
Copper test: rules copper in or out.
Activated carbon: removes many toxins after a suspected poisoning.
Dechlorinator: shrimp are more sensitive to chlorine than fish.
GH or GH/KH remineraliser: for soft or RO water.
Cuttlebone or mineral blocks: slow-release calcium.
Airline tubing and a valve: for drip acclimation and slow water changes.
Sponge filter: safe for baby shrimp and grows biofilm.

How to prevent it

Start shrimp only in a mature, cycled tank.
Drip-acclimate new shrimp over one to three hours (see acclimation).
Keep water changes small and regular.
Keep sprays, soaps and flea treatments away from the tank (see soap).
Check every product label for copper.
Buy from sellers whose water is similar to yours.

Why it happened

Shrimp breathe through gills and molt their whole skin regularly, so they react quickly to anything in the water. Each molt is a risky moment: they need the right minerals to build a new shell and stable water while it hardens. Many chemicals that are harmless to fish, especially metals and insecticides, are deadly to crustaceans.

When to get help

Ask an experienced shrimp keeper, a local club or your fish store if deaths continue after you've stabilised the water, if you see odd growths or white fuzz on the shrimp, or if you can't find any cause. Bring your test results.

In the game

Multiple Tank Syndrome doesn't have a shrimp card yet. The Soapy hands card is a real shrimp killer, and shrimp count toward the Clean-up crew goal.