Axolotl Care · Essential Guide

What Your Pet Shop Didn't Tell You About Setting Up an Axolotl Tank

Thousands of axolotls are slowly being poisoned in brand new tanks right now. Their owners have no idea. Here is what is actually happening — and how to fix it.

Quick Answer

Fishless cycling means building a colony of beneficial bacteria in your filter before adding your axolotl. Dose your tank to 4ppm ammonia, test daily, and wait for both ammonia and nitrite to drop to zero within 24 hours on three consecutive days. The process takes 4 to 10 weeks. Never add your axolotl to an uncycled tank.

Jump to a section What is cycling? The nitrogen cycle Symptoms Emergency steps Test your tap water How to fishless cycle Water parameters FAQ

The thing no one tells you when you buy an axolotl

You bought an axolotl. You set up the tank, filled it with water, maybe let it sit for a day or two, and added your new pet. Exactly what the pet shop told you to do — if they told you anything at all.

Here is the problem. That tank is not ready. The water looks clean. It smells fine. But it is slowly building up a level of toxic ammonia that your axolotl's body cannot handle — and without a cycled tank, there is nothing in that water to break it down.

This is not a rare edge case. This is what happens to the majority of axolotls sold in pet shops across the UK. The staff either do not know about cycling, do not have time to explain it, or assume you already know. Most new owners do not find out until their axolotl starts showing symptoms — by which point real damage may already be done.

This page exists to give you what you should have been told on day one.

What does "cycling a tank" actually mean?

Every time your axolotl breathes, eats, and produces waste, it releases ammonia into the water. Ammonia is highly toxic. In an uncycled tank, it has nowhere to go — it just builds up.

Cycling a tank means establishing a colony of beneficial bacteria in your filter that can process that ammonia before it reaches dangerous levels. These bacteria convert ammonia into nitrite — also toxic — and then a second group converts nitrite into nitrate, which is relatively harmless at low levels and removed through regular water changes.

This process — the nitrogen cycle — happens naturally. But it takes time. Usually four to ten weeks. And until it is fully established, your tank water is not safe for your axolotl.

Fishless cycling means going through this process before adding your axolotl — using ammonia to feed the bacteria without putting a living animal in harm's way. It is the right way to do it. And it is what this guide is going to walk you through.

The nitrogen cycle, simply explained

Axolotl waste produces

Ammonia (NH₃)

→

Bacteria convert to

Nitrite (NO₂)

→

Bacteria convert to

Nitrate (NO₃)

→

Removed by

Water Changes

Ammonia and nitrite are both acutely toxic to axolotls. Nitrate is tolerable at low levels — under 20ppm is your ceiling, and 5–10ppm is what you actually want — and kept in check with regular partial water changes. The goal of cycling is to have enough bacteria in your filter to process ammonia and nitrite as fast as they are produced.

In a brand new tank, those bacteria do not exist yet. They take weeks to colonise your filter media. That is the window during which your axolotl is at serious risk.

One thing worth understanding before you start, because it explains most of the frustration ahead: these are two separate colonies, and the second one is slower than the first. The bacteria that turn ammonia into nitrite establish first. The ones that turn nitrite into nitrate take longer to get going, and they cannot start until there is nitrite in the water for them to feed on. Almost everything confusing about cycling traces back to that lag.

Symptoms of an uncycled or poorly cycled tank

These are the signs that ammonia or nitrite is building up in your water. If your axolotl is showing any of these, test your water immediately.

🚫

Refusing to eat

⚖️

Unexplained weight loss

🌿

Pale or ragged gills

🍄

White fluffy fungal growth

🦴

Limb deterioration

😴

Lethargy or floating oddly

Important

These symptoms can have other causes — temperature, disease, stress. But if your tank is new or has not been properly cycled, water quality should be the very first thing you check. Test before you treat anything else.

Emergency: your axolotl is already in an uncycled tank

If your axolotl is already in the tank and you suspect the water is the problem, do not wait until you have finished reading this page.

🚨 Emergency steps — do these first

Test your water. You need an API Master Test Kit — not strips, which are inaccurate. Test for ammonia, nitrite, nitrate, and pH. If you do not have one, get one today.
Do a 30–50% water change immediately using dechlorinated water at the same temperature as the tank. This dilutes ammonia and buys your axolotl time.
Do not feed your axolotl while ammonia is elevated. Feeding produces more waste and makes things worse.
Tub your axolotl. This is the reliable option, and it beats anything you can pour into the tank. Move your axolotl to a clean food-grade tub of fresh dechlorinated water at the same temperature, deep enough to cover it, and do a 100% water change daily. That takes it out of the toxic water altogether rather than hoping to make the toxin safe. Keep it tubbed until the tank is genuinely fixed.
Repeat daily water changes of 30–50% until ammonia and nitrite both read zero on two consecutive tests.
Do not add treatments or medications until you know exactly what the water parameters are.

Once your axolotl is stable, work through the fishless cycling process below to establish your filter bacteria properly. Daily water changes are a sticking plaster — proper cycling is the fix.

A note on ammonia binders. You will be pointed toward products that claim to detoxify ammonia and buy you a safe window. We would not rely on one. The mechanism has never been published, there is no independent data behind the claim, and a standard ammonia test reads total ammonia including any supposedly bound form — so you cannot actually verify it worked. The real risk is behavioural: if you believe the ammonia is handled, you do fewer water changes. Remove the ammonia physically, or remove the animal.

Test your tap water before you start

Three numbers from your kitchen tap decide how this goes. Two of them you can fix cheaply. One of them you cannot fix at all once you have started, which is why this section is before the instructions rather than buried inside them.

1. Nitrate — check this one first

You will read in places that high tap nitrate stalls your cycle. It does not, quite. Your bacteria will not notice it and your cycle will finish in the same number of days either way. The problem arrives at the very end, and it is worse than a stall, because a stall you can fix.

A water change does not remove nitrate. It dilutes what is in the tank toward whatever is in your tap. So if your tap water carries 40ppm nitrate, then 40ppm is the floor of your tank, permanently. Carry buckets all week and you will go 100, then 70, then 55, then 47, then 44, closing in on 40 and never once getting below it.

An axolotl wants 5–10ppm. So the arithmetic is unforgiving:

The tap nitrate rule

Above roughly 5ppm nitrate in your tap water, you cannot finish this job with tap water alone. No amount of bicarbonate, patience or water changing touches it. You will need a nitrate reduction filter or RO water before that tank is safe to stock. Find out now, not in week six with a perfectly cycled filter and nowhere to go.

2. Hardness — this is what actually stalls cycles

Check whether your area has hard or soft water using the UK hard water map, then test your actual tap KH and GH, because the map is a regional average and your postcode may differ.

Hard water? You are lucky, and the process ahead is largely straightforward. Soft water is where cycles go to die, and the reason is worth understanding properly.

Carbonate hardness (KH) is your buffer against pH crashes. Processing ammonia consumes it — roughly 1.3 degrees of KH for every 4ppm dose your filter gets through. That is not a leak or a fault, it is the chemistry of what nitrifying bacteria do. Burn through your KH and pH falls, and below pH 7 the bacteria slow noticeably, and below 6.5 they effectively stop. They are not dead. They have downed tools, and they will not pick them back up until you fix the water. Aim to keep KH between 3 and 8 throughout, with bicarbonate of soda on hand.

General hardness (GH) is calcium and magnesium. It has no effect whatsoever on your cycle — the bacteria barely notice it — but it matters a great deal to your axolotl's gills, skin and bone. Aim for 8 to 14 before the animal goes in. If you are in a soft water area you will need to remineralise.

3. pH — where you are starting from

7.4 to 7.6 is ideal, and 7.0 to 8.0 is fine. If your tap water is already below 7 before you have dosed a drop of ammonia, sort that out before you begin rather than fighting it for six weeks.

How to fishless cycle your axolotl tank

This is the method we recommend for anyone setting up a new tank — or anyone whose tank has not been properly cycled yet. It takes anywhere from four to ten weeks. It requires patience. It is absolutely worth it.

What you will need

Pure ammonia — Dr Timms Liquid Ammonia or Knockout Household Ammonia. It must be clear, with no surfactants, dyes or perfume
NT Labs Aquarium Axo-Safe — dechlorinator, essential for every drop of water that enters the tank
API Liquid Freshwater Master Test Kit — liquid tests only, strips are not accurate enough
API KH & GH Test Kit — not optional in a soft water area
Sodium bicarbonate (baking soda) — for managing pH if it drops
A heater — optional, and the single best way to halve your waiting time
Bottled bacteria — genuinely optional. It can help a little, but anything promising a cycled tank in three to seven days is selling you something that is not possible
Somewhere to write your daily numbers down. A cycle you have not recorded is a cycle you cannot troubleshoot

Set up your tank, dechlorinate, and run the filter

Fill your tank and dechlorinate using NT Labs Axo-Safe following the bottle instructions. Chlorine and chloramine are in tap water specifically to kill bacteria, and bacteria are the entire thing you are trying to grow. Skip this and you will spend three weeks wondering why nothing is happening.

If you are using a heater, set it to 28°C — bacteria grow significantly faster in warmer water, which shortens the whole process. Nothing is living in the tank yet, so warmth is free speed. Run the filter continuously from this point. Never switch it off during cycling or you will kill the bacteria colonising the media.

Dose ammonia to 4ppm

4ppm is not arbitrary. It is roughly what one axolotl's waste output does to a tank, which means a filter that can clear 4ppm is a filter that can carry the animal. Aim lower and you build a colony too small for the job.

How many millilitres that takes depends on your tank volume and the strength of your ammonia, and the two common products are not interchangeable — Dr Timms is an ammonium chloride solution and Knockout is household ammonia, so the same number of millilitres gives you a different result. Work out your own dose with our ammonia dosing calculator rather than using a rule of thumb.

Test after an hour to confirm you are sitting at 4ppm. If you are using bottled bacteria, add it directly into the filter rather than the tank water.

Test pH and ammonia daily — and keep pH above 7

Using your API Master Test Kit, test pH and ammonia every single day. Aim to keep pH at 7.6 throughout. If it drops below 7 at any point, add a small spoon of bicarbonate of soda and retest in 30–60 minutes. Repeat until pH is back above 7.6. Low pH stalls the cycle — do not ignore it.

It may take 2–5 weeks before you see ammonia starting to come down. That is normal. Keep going.

Why your test looks stuck when it isn't

Your API card has steps at 0, 0.25, 0.5, 1, 2, 4 and 8ppm, and nothing in between. So it reads 4ppm until the true value falls below about 2.8, then jumps straight to 2. Your ammonia can be genuinely falling for the best part of a week before the card shows you anything at all. This is the single biggest reason people conclude their cycle has failed on day twelve. It almost certainly hasn't.

When ammonia starts falling, add nitrite to your daily tests

Once ammonia begins dropping, start testing for nitrite daily as well. Top ammonia back up to 4ppm any time it falls below that. Getting into a daily dosing routine makes it much easier — you will quickly learn exactly how much your tank needs.

Nitrite appearing is good news wearing a bad disguise. Nitrite is processed ammonia. Its arrival means stage one has worked.

When nitrite hits 5ppm, reduce ammonia dose to 2ppm

This step is important and often missed. Once nitrites spike to 5ppm, reduce your ammonia dose to keep it at 2ppm rather than 4ppm. Even if ammonia is dropping to 0ppm on its own, keep dosing to 2ppm — the bacteria still need something to feed on.

Here is why it matters. Every 4ppm of ammonia you process becomes roughly 11ppm of nitrite, and the bacteria that clear nitrite grow more slowly than the ones that made it. Keep hammering in full doses and you bury the tank faster than anything can empty it, and you will spend a month watching a purple test tube. Halving the dose keeps the first colony fed without burying the second.

Nitrite will still go off the top of the card. It is meant to. There is nothing alive in the tank to be harmed by it.

When nitrites start falling, dose ammonia back to 4ppm

Once nitrite begins coming down, increase your ammonia dose back to 4ppm. Continue until both ammonia and nitrite drop to 0ppm within a 24-hour period from your last ammonia dose.

When nitrite finally goes, it tends to go fast — a long plateau and then near enough nothing within a couple of days. That is the second colony overtaking what you are feeding it.

Cool the tank down slowly

If you used a heater, turn it off now and let the water cool gradually to 15–18°C, at no more than 1–2 degrees a day. Do not rush this — a rapid temperature drop can shock the bacteria and stall the cycle at the last hurdle. The colony survives the cool-down and simply works more slowly afterwards, which is fine. Once at temperature, dose ammonia to 4ppm and test after 24 hours.

The 3-day confirmation test

This is how you know the cycle is genuinely complete — not just nearly there. One clean morning is luck. Three is a cycled filter.

Day 1: Did ammonia and nitrite both drop to 0ppm? Yes — dose back to 4ppm. No — go back to step 6.
Day 2: Same question. Yes — dose back to 4ppm. No — go back to step 6.
Day 3: Both at 0ppm again? Your tank is cycled.

Do not be disheartened if you fail the first attempt or two, and expect to fail on nitrite rather than ammonia. By this stage ammonia disappears easily. Clearing all 11ppm of resulting nitrite inside 24 hours as well is what proves the second half of your filter is genuinely big enough. That is the whole point of the test.

Once all three days pass, test your nitrates — they will be very high, which is the receipt for all of this having worked. Dose a small amount of ammonia to keep the bacteria fed, then begin daily 50% water changes (dechlorinating each time with NT Labs Axo-Safe) until nitrates are down to 5–10ppm. From a typical finish that is about four or five changes if your tap water is clean. If your tap nitrate is 10ppm or higher, it is no number of changes — see the tap nitrate rule. At 5–10ppm, your tank is ready for your axolotl.

Speed up the process with seeding

You can significantly shorten cycling time by adding filter media from an already-cycled tank directly into your filter. Even a small piece of established sponge carries millions of the bacteria you need, and it skips the hardest part of the whole process, which is finding the first few thousand. Ask in axolotl keeping communities — many experienced keepers will share media. Keep it wet on the way home, because if it dries out it is worthless. You still need to go through all the steps above, but the timeline can shrink considerably.

You do not need to crank the bubbler up

Fishkeeping guides will tell you to run as much aeration as possible during a cycle, on the grounds that nitrifying bacteria need oxygen. They do need oxygen. They are just very unlikely to be short of it. Your filter is already returning water to the surface and agitating it continuously, and that surface movement is what actually drives gas exchange. Water at cycling temperature saturates quickly and stays there. Run an air stone if you like the look of it, but do not buy an air pump expecting a faster cycle, and do not go hunting for an oxygen problem when your numbers stall. Check KH and pH instead. That is where the answer nearly always is.

Safe water parameters for an axolotl tank

You cannot manage what you cannot measure. Liquid test kits are non-negotiable — strips are not accurate enough. The API Freshwater Master Test Kit covers ammonia, nitrite, nitrate and pH. Add the API KH & GH liquid tests as well, especially in a soft water area — they are the two numbers that decide whether your cycle finishes, and most people find out about them too late.

Parameter	Safe level	Danger level	Action
Ammonia (NH₃)	0 ppm	Above 0 ppm	Immediate water change; dechlorinate with NT Labs Axo-Safe
Nitrite (NO₂)	0 ppm	Above 0 ppm	Immediate water change; dechlorinate with NT Labs Axo-Safe
Nitrate (NO₃)	5–10 ppm ideal	Above 20 ppm	Partial water change to dilute. If your tap nitrate is high, you will need a nitrate filter or RO water
pH	7.4 – 7.6 ideal (7.0–8.0 acceptable)	Below 7.0	Add small spoon of bicarbonate of soda; retest in 30–60 mins
KH (carbonate hardness)	3 – 8 °dKH	Below 3	Bicarbonate of soda. This is your buffer against a pH crash
GH (general hardness)	8 – 14 °dGH	Below 6	Remineralise. Matters for gills, skin and bone, not for cycling
Temperature	15°C – 18°C	Above 21°C	Cooling fan, frozen water bottles, tank chiller

Test weekly once your tank is established. If anything reads outside the safe zone, switch to daily testing until it resolves. Water problems are invisible until they are serious — do not wait for symptoms.

Frequently Asked Questions

How long does fishless cycling take?

Anywhere from four to ten weeks from scratch depending on your water hardness, temperature during cycling, and whether you use seeding media. With a heater at 28°C and established filter media it can be considerably faster. Without either, expect the longer end of that range. Do not rush it — an incomplete cycle is worse than a longer wait.

Can I add my axolotl before the cycle is complete?

Only if you have no choice and are prepared to do daily 30–50% water changes to keep ammonia and nitrite from reaching dangerous levels. Dechlorinate every change with NT Labs Axo-Safe. It is stressful for the animal and exhausting for you. The right answer is to wait.

Why does my pH keep dropping during cycling?

Because processing ammonia consumes carbonate hardness. Roughly 1.3 degrees of KH disappears for every 4ppm dose your filter gets through, and KH is what holds your pH steady. This is chemistry rather than bad luck, and it hits soft water areas hardest. Add a small spoonful of bicarbonate soda, wait 30–60 minutes, and retest. Repeat until pH returns to 7.6. If you are in a soft water area and struggling, get in touch — it gets complicated, and there are specific steps to follow.

My ammonia won't drop to zero — what's wrong?

Either the bacterial colony is not large enough yet, your pH has dropped below 7 (which stalls bacterial activity — check it, and check KH while you are there), the temperature is too low, or you have been doing large water changes and removing the ammonia before the bacteria can process it. Check pH and KH first, then temperature, then keep the filter running and be patient.

My nitrites went off the chart — what do I do?

Reduce your ammonia dose to 2ppm and hold it there. Do not do large water changes to try to bring it down — just reduce the ammonia input and let the bacteria catch up. This is exactly why you drop to 2ppm when nitrite hits 5ppm during step 5. And remember there is nothing alive in the tank to be harmed by it, so it is not an emergency, however alarming the colour looks.

Do I need to do water changes during cycling?

Generally no. The ammonia and nitrite are feeding your developing bacteria, and there is nothing alive in there to protect. Every litre you tip out is ammonia you paid for and will have to dose straight back in. It does not damage your cycle — your bacteria live in the filter media rather than the water, so you cannot rinse them away — it just wastes your time. If pH or KH is the problem, bicarbonate of soda fixes it without emptying the tank. Save the water changes for the end, when there are a lot of them.

Does high nitrate in my tap water affect cycling?

It will not slow your bacteria down at all, but it decides whether you can finish. A water change dilutes the tank toward your tap value rather than toward zero, so your tap nitrate is a permanent floor. If your tap is 40ppm, your tank can never go below 40ppm no matter how many buckets you carry. Axolotls want 5–10ppm, so above roughly 5ppm in your tap water you will need a nitrate reduction filter or RO water before the tank is safe to stock. See test your tap water.

Do I need an air pump or bubbler to cycle a tank?

No. Nitrifying bacteria do need oxygen but are very unlikely to be short of it. Your filter returns water to the surface and agitates it continuously, and that surface movement is what drives gas exchange. Water at cycling temperature saturates quickly and stays there, so an air stone bubbling through already saturated water adds little on top. Run one if you like the look of it, but do not expect it to speed anything up.

What KH and GH should an axolotl tank have?

KH between 3 and 8, GH between 8 and 14. KH is your buffer against pH crashes and is the number that decides whether your cycle finishes at all. GH is calcium and magnesium, which has no effect on cycling but matters for gills, skin and bone. If you are in a soft water area you will need to remineralise before your axolotl goes in.

My tank was cycled but now ammonia is spiking again — why?

Most common causes: the filter was switched off even briefly, filter media was rinsed in tap water rather than tank water (chlorine kills the bacteria instantly — always use tank water to rinse media), too many new animals added at once, or something has died and is decomposing in the tank. Test, do a water change with Axo-Safe, and find the cause.

Do I need to dechlorinate tap water every time?

Every single time, without exception. Chlorine and chloramine are in tap water specifically to kill bacteria, and bacteria are the entire thing you are growing.

And read the ingredients, because this is where axolotls part company from fish. Your dechlorinator must contain no iodine, no aloe vera, and nothing labelled "herbal extracts". Iodine was historically used in laboratories to force axolotls through metamorphosis — a painful process, and not one worth risking accidentally. Aloe vera and herbal additives interfere with the slime coat they use to absorb nutrients through their skin. NT Labs Axo-Safe is formulated specifically for axolotls and contains none of them.

What temperature should my axolotl tank be once cycling is done?

15–18°C is the target range for a cycled axolotl tank. Cool the tank down slowly after cycling, at no more than 1–2 degrees a day — a rapid drop can shock the bacteria. Sustained periods above 19°C raise the risk of fungus and illness, and above 21°C is a serious emergency. UK summers can be problematic — a fan over the tank surface or a purpose-built aquarium chiller are your options.

Ready to sort your axolotl's diet too?

Once your tank is cycled and your axolotl is settled, the next question is feeding. Our complete feeding guide covers every life stage — from hatchling to adult.

Read the feeding guide →