Fish: moving house with an aquarium without losing the cycle

Quick answer

Moving an aquarium is not a fish problem, it is a bacteria problem. The nitrifying bacteria that keep ammonia and nitrite out of the water live in the filter media and on surfaces, not in the water itself, and they die if they dry out or run out of oxygen.

That single fact reorganises the whole job. The water you are so carefully saving is the least valuable thing in the tank. The wet, oxygenated filter media in a bucket beside you is the most valuable, and if it survives the move intact, most of the rest is manageable.

• The bacteria are in the media and on surfaces, not in the water.
• Never seal filter media in a plastic bag for a long journey. It goes anoxic and the bacteria die.
• Never move a tank with water, substrate or decor still in it. Glass tanks are not built for that.
• Test the tap water at the new address before you fill, because water chemistry changes between areas.
• Expect a mini-cycle afterwards and test ammonia and nitrite daily for a fortnight.

Betta fish in a planted aquarium

Decide in 60 seconds

Why the water is not the point

Ask most aquarists what to save when moving a tank and they will say the water. It is the wrong answer, and it costs people a great deal of effort with buckets.

The bacteria that convert ammonia to nitrite and nitrite to nitrate are attached organisms. They colonise surfaces with flow over them, which in practice means the filter media above all, then the substrate, the decor, the glass and the plants. The free-floating population in the water column is small.

What saving old water actually does is preserve chemistry continuity: the pH, hardness and dissolved mineral content the fish are used to. That is genuinely worth something, particularly if you are moving to an area with different tap water, and it is a reason to take a couple of large containers of tank water rather than a reason to take all of it.

The media is different. Nitrifying bacteria are aerobic, and a sealed bag of wet media consumes its dissolved oxygen within a few hours. After that the colony begins to die and the by-products of that die-off are themselves polluting. Media must travel wet, in tank water, in an open or loosely covered container, and on a long journey it should have an air stone running in it.

The same applies to sponges, ceramic media, bio-balls, matrix and the biological cartridge in a hang-on filter. Keep it wet, keep it in tank water, keep it aerated, and do not rinse it in tap water at any point, because chlorine kills the colony directly.

The plan, from two weeks out

Two weeks before.

Stop adding new fish, plants or invertebrates. You want a stable system going into the move, not one that is still settling.

Service the filter now if it is due, so that it is clean and functioning and does not need attention on moving day.

Gather the equipment: several clean food-grade buckets with lids, fish bags or lidded containers, a battery-operated air pump with airline and air stones, a siphon, a large towel or blanket for the tank, dechlorinator in a generous quantity, and a water test kit.

If you are moving to a different water supply area, find out what comes out of the tap there and test a sample if you can get one.

One week before.

Do a water change and confirm the parameters are good. Reduce feeding slightly.

Decide what happens to the substrate, particularly if it is deep and old.

Arrange for the tank to be one of the first things moved into the new place rather than the last, so it can be set up while there is still daylight and patience.

Two days before.

Final water change.

Stop feeding. A day or two of fasting is well tolerated by most species and substantially reduces the waste produced in transport containers, which is the main thing that fouls the water fish are travelling in.

Moving day, in order

1. Unplug the heater and leave it in the water to cool.

A hot glass heater lifted into air can crack, and a cracked heater is both a loss and an electrical hazard. Unplug it, wait, then remove it and wrap it.

2. Catch and bag the fish.

Use tank water. Give each container plenty of air space above the water, more than you think, because gas exchange at the surface is what keeps them alive. Fewer fish per container is better. Keep aggressive or fin-nipping species separate.

Cover or darken the containers. Fish in the dark are calmer, and calm fish use less oxygen.

For a long journey, run an air stone from a battery pump.

3. Move plants and decor into buckets of tank water.

They carry bacteria too, and plants suffer badly if allowed to dry.

4. Get the filter media into a bucket of tank water.

This is the critical step. Open the filter, take the biological media out, and submerge it in tank water in a bucket. Do not rinse it. Do not squeeze it dry. Do not put it in a sealed bag. On a long journey, put an air stone in with it.

Take the filter body separately.

Betta fish in a tank

5. Drain the tank completely.

Every last centimetre. Then remove the substrate into buckets, or dispose of it if you have decided to replace it.

6. Move the tank empty.

Never move a tank with anything in it. A tank supported at the corners with weight inside flexes the base, and the seams are the part that fails. Carry it from underneath, not by any frame or top bracing. Transport it flat and level on a padded surface, not on its side or end, and pad the corners.

7. Level the stand before the tank goes on it.

Use a spirit level, on both axes. A tank on an unlevel or unsupported stand carries uneven stress across its base and seams, and that is one of the more common causes of a tank failing weeks after a move rather than during it.

8. Rebuild in order.

Substrate first, then hardscape and decor, then fill with dechlorinated water at approximately the right temperature. Fill slowly onto a plate or a bag to avoid excavating the substrate.

Reinstall the filter with the original media and start it. Fit the heater and let the temperature stabilise.

9. Acclimate the fish back in.

Float the containers to equalise temperature, then add new water to them gradually before releasing the fish, particularly if the new tap water differs from the old. Do not tip transport water into the tank.

10. Do not feed on the first day, and feed lightly for the next few.

The new address may not have the same water

This is the part that catches people moving any real distance.

Tap water differs by supply area in hardness, pH, nitrate content, and whether the utility uses chlorine or chloramine. Chloramine is more stable than chlorine and does not gas off, so a dechlorinator that handles chlorine only is not sufficient where chloramine is used.

Soft-water species, shrimp, and anything sensitive to hardness can be seriously affected by a change in general hardness or carbonate hardness. If the new water is very different, the sensible approach is a gradual transition over subsequent water changes rather than a single wholesale swap, which is another reason to bring a couple of containers of old water.

Test the new tap water for pH, hardness and nitrate before you fill the tank. Some supplies carry enough nitrate that it is worth knowing before you conclude the tank is polluted.

For reef and soft-water systems, plan for reverse osmosis water and remineralisation at the new address, and confirm you can get it locally.

The fortnight after

Expect a mini-cycle. Even a well-handled move disturbs the biological filter, and a small ammonia or nitrite reading in the first week is common.

Test ammonia and nitrite daily for at least two weeks. Act on any detectable reading with increased aeration, reduced feeding, and small daily water changes with dechlorinated water at temperature.

Keep feeding light. Every meal is ammonia.

Do not clean the filter, do not vacuum the substrate hard, and do not do anything else that removes bacteria.

Do not add new livestock for several weeks.

Watch for white spot. Transport and relocation are classic triggers, and it typically appears several days after the stress rather than immediately.

Watch the seams and the stand. Check for damp underneath the tank daily for the first week.

Betta fish in an aquarium

Marine and pond systems

Marine. Live rock must stay wet and cool, and it must not be allowed to sit in warm stagnant water, because the die-off of organisms in and on it produces a large ammonia load. Expect to test heavily afterwards. Corals need to remain submerged, and prolonged darkness harms photosynthetic species, so plan the timeline around them. Check salinity at both ends, and remember that evaporation during a slow move raises it.

Ponds. This is a different job and often a professional one. Fish need holding tanks with aeration, the pond has to be drained progressively rather than in one go, and the sludge at the bottom carries an enormous oxygen demand. If the pond contains large koi, handling them safely without injuring them or yourself needs equipment and experience.

International moves. Live animal import rules vary widely and many species cannot be moved across borders. Establish the legal position months in advance, and consider rehoming the livestock locally and rebuilding at the new address, which is often kinder than a very long journey.

Where the usual advice goes wrong

"Save as much old water as possible."

The water carries chemistry, not bacteria. Two large containers are useful. Ten are a waste of effort that could have gone into keeping the media alive.

"Put the filter media in a sealed bag so it stays wet."

It stays wet and runs out of oxygen. Use an open bucket of tank water instead.

"Rinse the media in tap water so it is clean for the new tank."

Chlorine or chloramine in tap water kills the bacteria you are trying to preserve. If media must be rinsed, rinse it in old tank water.

"You can move the tank with the gravel in, it is only a short distance."

A tank flexes when supported unevenly with weight inside, and glass seams do not forgive it. The failure often happens weeks later, at the new address, with fish in it.

"Move the fish in a bucket of fresh tap water so it is clean."

Untreated tap water on gill tissue is directly damaging. Transport in tank water.

"Feed them well before the journey so they are not hungry."

Fed fish produce waste in the bag. Fast them for a day or two instead.

What to have ready

Clean food-grade buckets with lids, more than you think.

Fish bags or lidded transport containers, and an insulated box to keep them at a stable temperature.

A battery air pump, airline and air stones, tested before the day.

Dechlorinator, in quantity, and one that handles chloramine if your new supply uses it.

A water test kit that is in date.

A spirit level.

A siphon and a fine net.

Towels, padding and a blanket for the tank.

A thermometer for the transport containers as well as the tank.

What never to do

Do not move a tank with water, substrate or decor inside it.

Do not seal filter media in a plastic bag.

Do not rinse media in tap water.

Do not lift a tank by its top frame or bracing.

Do not put a tank on a stand you have not levelled.

Do not transport fish in untreated tap water.

Do not add all the fish back before the temperature and the dechlorination are confirmed.

Do not clean the filter, vacuum the substrate or add new fish in the fortnight after the move.

When to get help

Seek advice from an aquatic specialist or an aquatic vet the same day if fish are gasping after the move, if ammonia or nitrite is high, or if you have significant losses in the first days.

Seek advice in advance for marine and reef systems, for ponds, for large or heavy tanks, and for any move long enough that the animals will be in transport containers overnight.

Seek advice before the move if you are relocating to an area with markedly different water, particularly with soft-water species, shrimp or a reef system.

Seek advice promptly if white spot or another disease appears in the week after the move, because a stressed population in a partly disrupted biological filter needs treatment chosen carefully.

Have ready your species list and stocking level, tank volume, the old and new tap water test results, how long the move took, how the media was transported, current ammonia, nitrite, nitrate, pH and temperature, and what you have done since arriving. In a marine system add salinity before and after.

Betta fish swimming in a tank