How to cycle a tank for shrimp

Don't add shrimp until ammonia and nitrite both read 0 mg/L on a liquid test kit, and the tank has grown a visible film of bacteria and algae on the hardscape (rocks and wood). For most setups that is four to eight weeks, not four to eight days. A tank that looks clean is not the same as a tank that is safe.

What the nitrogen cycle actually is

Everything that lives or dies in your tank produces ammonia: waste, uneaten food, a melting leaf, a dead snail. Free ammonia is toxic at very low concentrations, and a tank only becomes liveable once microbes are eating it.

1. Total ammonia accumulates. Your kit reads total ammonia nitrogen: free ammonia (NH3) and ammonium (NH4+) together. At the pH most shrimp tanks run, nearly all of it is ammonium.
2. Ammonia-oxidising microbes convert ammonia to nitrite (NO2-). Bacteria and ammonia-oxidising archaea are both reported to do this in aquaria. Nitrite is also toxic, and this is where people declare victory early because ammonia is falling.
3. Nitrite-oxidising microbes convert nitrite to nitrate (NO3-). Nitrospira is the genus usually credited in freshwater aquaria, and some (comammox) appear to do the whole conversion alone. Nitrate is far less toxic, and leaves via water changes and plant uptake.

Those microbes live on surfaces, not in the water column (the open water), so water changes during cycling do not reset your progress. What does wreck a cycle: rinsing filter media under an untreated tap, leaving a filter unpowered until it goes anoxic (starved of oxygen), or dosing antibacterials.

Two details matter more for shrimp than for fish. The toxic form is free NH3, and its share rises with pH and temperature, so 0.5 mg/L total ammonia is more dangerous in a Neocaridina tank at pH 7.6 than in a Caridina tank at pH 6.2. Low pH buys margin, not immunity. And nitrification (that ammonia-to-nitrate work) consumes carbonate hardness (KH), so on low-KH active soil a heavy cycle can drag pH down over weeks. Track KH as well as pH.

Why shrimp are less forgiving than fish

A hardy fish survives an ammonia blip and tells you by gasping at the surface. Shrimp don't warn you: they stop grazing, sit still, and then you find one dead after a moult.

• Moulting is the vulnerable window. A shrimp that has just shed its exoskeleton (outer shell) is soft and stressed, and a problem a settled shrimp shrugs off can kill a moulting one.
• Nitrite appears to affect crustaceans differently to fish. Shrimp carry oxygen on haemocyanin (a copper-based blood protein), not haemoglobin, and nitrite is reported to interfere with oxygen transport and moulting in crustaceans; published data for Neocaridina davidi is thin, so assume invertebrates are no more tolerant than fish.
• The obvious fix is itself a stressor. A large emergency water change swings TDS, GH and temperature at once, and shrimp mind sudden parameter movement more than a slightly high number.

So the target for ammonia and nitrite is 0 mg/L. Not low. Not "0.25 mg/L is basically fine". An uncycled or half-cycled tank is the first thing to rule out when shrimp start dying with no obvious cause.

The only two numbers that matter: 0 and 0

Use a liquid reagent test kit, not paper strips, which are widely reported to be unreliable at the low end of these ranges. Nitrate confirms the second group of microbes is working.

The test that proves a cycle is a 24-hour turnover test. Dose ammonia to a known concentration (2 to 4 mg/L is the fish-keeping convention; many shrimp keepers use 1 mg/L), then test 24 hours later. If ammonia and nitrite both read 0 mg/L, the tank processed the lot in a day. Repeat on three consecutive days.

One gotcha: dechlorinators (tap-water conditioners) that claim to detoxify ammonia are generally understood to bind it rather than remove it, and common kits are reported to still read that bound ammonia, so an alarming number can come from water that isn't dangerous. Check whether your supply is chlorinated or chloraminated, too (chloramine is the longer-lasting form of chlorine some supplies use).

Biofilm is the first food, not a nice-to-have

Biofilm (the thin film of microbes and algae that coats every wet surface) is the baseline diet rather than a supplement, and the only food a newly arrived juvenile can reliably get at, which our guide to feeding shrimp covers in full.

To grow it deliberately, run your lights on a normal schedule, add live plants early, and put botanicals (dried leaves, cones and seed pods) in from day one. Indian almond (catappa) leaves, alder cones and cholla wood all give shrimp something to graze as they break down, and a pinch of food in the empty tank doubles as an ammonia source. A dull brown cast on the glass is a good sign, so don't scrub it off the day before your shrimp arrive.

A realistic timeline

Stage	Roughly	What you should see
Setup and seeding	Week 0 to 1	Plants and botanicals in, ammonia source started. Ammonia climbing, nitrite 0 mg/L.
Ammonia processing begins	Week 1 to 3	Ammonia falling, nitrite appears and climbs. The longest phase.
Nitrite falls away	Week 3 to 5	Nitrite drops to 0 mg/L, nitrate appears. Start the 24-hour test.
Maturing	Nitrite drop to about week 8	Biofilm visible, plants rooted, GH, KH and TDS steady week to week.

Seeded media (filter material moved across from an established tank) compresses the first three stages, not the last. Biofilm takes the time it takes.

Cycling through an Australian winter

It is late winter here, and that changes the maths. An unheated tank in a Melbourne lounge room tracks the overnight low, which usually runs from single figures to the mid teens at this time of year, and nitrifying microbes work more slowly when it is cold, so cycling can take longer than the table suggests, though the exact temperature response isn't well established. Run a heater at 22 to 24 °C for the cycle, then settle back to your usual temperature; Neocaridina davidi is commonly kept between about 18 and 28 °C, with 20 to 24 °C the sensible target, though those outer bounds are hobby consensus rather than hard limits. Our guide to keeping shrimp through an Australian winter covers the cold-water slowdown in detail.

We ship livestock on Mondays and Tuesdays, so your tank needs to be finished before you order, not while the box is on its way. Cold shock is the live risk this time of year, not heat.

Where keepers genuinely disagree

• Bottled bacteria. Some keepers find it shaves a week or two off, others see no difference.
• Cycled versus matured. A tank can pass the 24-hour test at four weeks and still be a poor home for juveniles because there is nothing to graze. Some keepers wait two to three months; those running seeded, heavily planted setups often go earlier and report no trouble.

How to know you're ready

• Ammonia 0 mg/L and nitrite 0 mg/L, 24 hours after dosing, three days running.
• Nitrate present but modest, and coming down with water changes.
• GH, KH and TDS steady across a full week with no dosing adjustments.
• Visible biofilm and diatoms (brownish micro-algae) on glass, wood and leaves.
• Temperature stable, not swinging several degrees overnight.

Our Neocaridina are raised in remineralised Melbourne tap water, input TDS around 60 ppm, dosed to about 160 ppm TDS; matching that closely makes the move easier. Bee-type Caridina are commonly kept softer, roughly 100 to 150 ppm TDS with KH at or near 0 dKH on active soil, and tigers (Caridina mariae) harder again. Crystal red and crystal black are usually placed in Caridina logemanni, though many listings still file them under C. cantonensis and the placement is contested; Taiwan Bee lines sit in C. cantonensis. See our guide to water parameters for Caridina and Taiwan Bee shrimp.

Adding the shrimp

Drip-acclimatise (introduce your tank's water a drip at a time) over a couple of hours, don't tip bag water into the tank, and leave the lights off afterwards; the full method is in our Shrimp Care and Acclimation Guide. If something goes wrong on arrival, our DOA and Missing Items Policy asks for a claim within 8 hours of delivery, with photos and a short video of the animals in the unopened bag. The remedy is replacement or refund of livestock value, your choice.

The grading on our listings runs from Entry, Mid, High and Collector and describes appearance only. It is explicitly not a health rating.

None of this is technically difficult, just slow. The usual failure mode is impatience.