How to cycle a new shrimp tank, week by week

Published October 19, 2026 · Updated October 19, 2026 · 6 min read

Young stem plants and Anubias growing between rocks on dark substrate in an aquarium — Photo: Indonesiagood, Wikimedia Commons, CC BY 4.0 (cropped)

Quick answer

Cycling grows the bacteria that turn toxic ammonia into much less harmful nitrate. Without them, waste builds up and kills shrimp.
Most guides say a fishless cycle takes about 4 to 8 weeks.
Add a measured source of ammonia, and test every day or two.
The cycle is done when ammonia and nitrite read 0 within a day of adding ammonia, and nitrate shows up.
Do a large water change before the shrimp go in. Many guides suggest waiting a little longer so food can grow on the surfaces.

What cycling is

Shrimp waste, leftover food and dead plant leaves all release ammonia. Ammonia is toxic, even in small amounts. In a mature tank, two groups of bacteria deal with it. The first group turns ammonia into nitrite, which is also toxic. The second group turns nitrite into nitrate, which is much less harmful. Water changes and plants remove the nitrate.

This chain is called the nitrogen cycle. A new tank has almost none of these bacteria. Cycling means growing them before any shrimp go in. They live mostly on surfaces, above all in the filter sponge.

With shrimp, the usual method is a fishless cycle. Instead of animals, you add a measured amount of ammonia to feed the bacteria.

Before you start

Set up the tank, substrate and filter, and fill the tank with water treated with conditioner. Chlorine and chloramine in tap water also kill these bacteria.
Keep the filter running all the time. Most of the bacteria will grow in it.
Get a test kit for ammonia, nitrite and nitrate.
Choose an ammonia source. Bottled ammonia sold for fishless cycling is the easiest to measure. Use one without added scents or soap.
Check the substrate. Active soil releases ammonia by itself for the first weeks or months. Test before you add any more.
Keep the water warm if you can. Shrimp and Snail Breeder suggests about 27 °C (80 °F) during the cycle, because warmth speeds up the bacteria.
Watch the pH. The same guide warns that the bacteria slow down if pH drops below about 6.5. pH is the scale of how acidic the water is.

Week by week

Ammonia is measured in ppm (parts per million). Fritz, a maker of bottled ammonia, says to bring the tank to about 2 ppm. Shrimp and Snail Breeder doses up to about 5 ppm. Both warn that much more than that slows the cycle down.

When	What happens	What to do
Day 1	The tank has almost no bacteria yet.	Add ammonia to about 2 ppm. Test the next day.
Week 1	Ammonia stays high. The first bacteria start to grow.	Test every day or two. When ammonia drops, top it back up to about 2 ppm.
Weeks 2 to 3	Ammonia starts to fall. Nitrite appears and rises.	Keep adding ammonia. If ammonia or nitrite climbs above 5 ppm, skip a dose.
Weeks 3 to 6	Nitrite stays high for a while, then drops quickly. Nitrate rises.	Keep going. This stage often takes the longest.
Weeks 4 to 8	Ammonia and nitrite both read 0 within a day of a dose.	The cycle is done. Move on to the water change.

These weeks are typical, not fixed. Every tank is different, and a tank seeded with old filter media can finish much sooner.

Ways to speed it up

Seed it with mature filter media. A squeezed sponge or used filter media from a healthy, established tank brings a ready-made group of bacteria. This is usually the fastest way.
Add bottled bacteria. Live nitrifying bacteria are sold in bottles. Shrimp and Snail Breeder adds them on the first day of its fishless cycle.
Plant early. Live plants bring helpful bacteria with them and take up some of the waste.
Keep it warm, and keep pH above about 6.5.

Do not clean the filter during the cycle, and never rinse filter media in untreated tap water.

How to tell it is done

Aquarium Co-Op describes a cycled tank as one that reads 0 ppm ammonia, 0 ppm nitrite and some nitrate. Shrimp and Snail Breeder adds that the zero readings should hold for more than a couple of days in a row.

A simple test: add your usual dose of ammonia, wait 24 hours, and test. If ammonia and nitrite both read 0 and nitrate shows up, and this is true for a few days in a row, the bacteria can keep up.

After the cycle

Do a large water change. After a fishless cycle, nitrate is often very high. Shrimp and Snail Breeder suggests changing 80 to 90 percent of the water, with conditioned water. Aim for nitrate under about 10 to 20 ppm before shrimp go in.
Stop adding ammonia once the shrimp are in. From then on, their waste and food feed the bacteria.
Give it a little more time. Shrimp graze on biofilm, a thin coat of bacteria, algae and other tiny life on every surface. A brand-new tank has little of it. Shrimp Science suggests waiting about 6 to 8 weeks in total, and Shrimp and Snail Breeder at least a few weeks after the cycle.
Add the shrimp slowly. Read how to buy healthy shrimp and how to acclimate them.

After that, keep testing nitrate regularly. The water parameters guide lists the numbers to aim for.

FAQ

How long does it take to cycle a shrimp tank?

Most guides say about 4 to 8 weeks for a fishless cycle. Seeding the filter with media from an established tank can make it much faster. Shrimp Science suggests letting tanks with active soil cycle and mature for a couple of months.

Can I add shrimp during the cycle?

No. Ammonia and nitrite are toxic to shrimp, even at low levels. Wait until both read 0 within a day of adding ammonia, then do a large water change before the shrimp go in.

How much ammonia should I add to cycle a tank?

Fritz, a maker of bottled ammonia, says to bring the tank to about 2 ppm. Shrimp and Snail Breeder goes up to about 5 ppm. Both warn that more than that slows the cycle. Tanks with active soil may release enough ammonia on their own, so test first.

Sources

Aquarium Co-Op: The Beginner's Guide to the Nitrogen Cycle for Aquariums
Aquarium Co-Op: Fritz Fishless Fuel (dosing directions)
Shrimp and Snail Breeder: Cycling Your Shrimp Aquarium Fishless
Shrimp and Snail Breeder: Basic Shrimp Tank Setup for Neocaridina
Shrimp Science: The Beginner's Guide to Freshwater Shrimp Tanks
Shrimp Science: The Guide to Substrates for Shrimp Tanks
Shrimp Science: How to Clean a Sponge Filter

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