How to Reset a Fish Tank: Complete Guide

In many ways, resetting a fish tank is harder than setting up a new one. Regardless of its age, an aquarium has many inhabitants. Dismantling their home takes considerably more planning and effort than laying the substrate and filling up a new tank with water.

The six key steps in every tank reset are as follows:

• Removing livestock and keeping it alive in a temporary container
• Removing live plants and storing them for 7-10 days
• Removing and cleaning hardscape; depending on hardscape condition or personal preference, some of it can be replaced
• Removing and cleaning substrate; depending on its state or personal preference, parts of the substrate or all of it can be changed
• Taking care of the filters

There are many aspects to these four processes. Each requires several steps, some obligatory, some based on intentional choice. For example, if you are relocating the aquarium to a new place you may prefer to have it going again as soon as possible. If it is a new tank, you may not clean the substrate at all.

If the tank has existed for months, a good rinsing will do. But if you want to get rid of pest snails, you will have to treat it with boiling water and/or hydrogen peroxide. Changing the entire substrate is also not out of the question, but pest snails are likely to hang out on plants.

And plants are probably the trickiest customers when it comes to aquarium reset. I usually remove them first, as a tank without plants allows for much easier catch of its livestock.

Store the Plants Safely During the Reset

Storing aquarium plants is not a thing for most fishkeepers. We buy them and unpack them pretty much right away. New plants should undergo quarantine to ensure they are pest-free. But in quarantine, most of us usually keep a handful of plants.

Removing all the plants from a planted tank and putting them into a bucket or hospital tank could destroy many species. Plants feed mostly through the water column, but the water column of a functioning tank is enriched by fish waste and decaying matter.

Many plants clustered together, uprooted, will create mayhem with the water of an empty hospital tank or large bucket. Frequent water changes could offset the effects but keeping many plants alive solely in water is tough and unnecessary.

The safe way to store live plants during a tank reset is to keep them very moist and somewhat separated.

In good conditions, sensitive plants can survive over a week, and more durable species over 10-14 days. The ideal storage conditions for aquarium plants are:

• Low temperature — Keep the plants at the lowest temperature range they can tolerate. 16° to 20°C or 60° to 68°F work for most plants. Freshwater aquariums house only cold-blooded species and plants are no exception: low temperatures slow their metabolism. Slow metabolism is beneficial in preservation as plants use less energy 
• Moisture — All water plants need is ample moisture. No need to keep them submerged but keep them well-watered.

Plastic bags and boxes are good containers for aquatic plants. I like to separate the plants and lay them across the bottom of plastic boxes. The covers keep moisture inside.

I keep plants from the same or similar species in the same container for easier watering. While separating individual plants, I check the health of their roots. Signs of decay, soft edges, or roots with any other color than ivory white indicate different deficiencies.

Remove Livestock

During an aquarium restart or relocation, fish, snails, and shrimp should go to a hospital tank. It could be a proper aquarium or a bucket.

Fill up the recipient vessel with water from the original tank, to prevent unwanted stress or shock of your aquatic pets.

Make sure the temperature in the hospital tank is the same. Add filtration and you are good to go. You can use a filtration medium — sponge or other media — from the old tank in order to keep the nitrogen cycle going.

In case you are resetting the original tank because of a disease, make sure to cycle the hospital tank for at least 10 days before adding livestock to it. In such scenarios, using water from the sick tank won’t be a good idea, so acclimatizing the livestock to the hospital tank is essential.

Shrimp are particularly sensitive to water changes, so dip-water acclimatization is the safest option for them.

Removing and Replacing Substrate

Substrate is another major point of consideration during aquarium reset. If you are keeping the same substrate, things are considerably simpler.

All you have to decide is how much you are going to clean it. I’ll always recommend a good rinse under running water, at the very least.

More in-depth cleaning, with hydrogen peroxide, vinegar, or boiling is necessary when dealing with illnesses or when the substrate is very old, indeed. The upside is that you get a clean beginning, a total reset of the ecosystem. The downside is that all microbial life would be gone.

You must decide which option suits your needs best and go for it.

Now, if you are replacing inert substrates like gravel with sand, the complexity doesn’t change much. Make sure the new substrate is as clean as it gets to reduce any issues with cloudy water and you are good to go.

Things become considerably more complex when dealing with active substrates.

Replenishing Active Substrates During Aquarium Restart

If you are simply moving the tank and the active substrate is relatively new, you can use it without an issue. But commercially sold enriched substrates and potting soils deplete over time. Most brands will gradually lose their nutritive powers over 10-16 months.

Resetting a tank with new aquasoil is tricky because these products release high amounts of ammonia in the first few weeks. This makes them dangerous for most fish and shrimp, as well as for delicate plants that cannot tolerate much ammonia.

It takes more than a week (a few weeks, actually) of regular water changes to bring aquasoils with high ammonia concentrations to safe levels.

One way of dealing with the issue is by mixing in some new aquasoil with the old one. (I’d recommend cleaning the old one by rinsing it thoroughly before reusing it.) Root tabs are another way to go.

Lastly, you can use new aquasoil or topsoil at the very bottom and cap it with an inert substrate like sand or the old, depleted aquasoil. This way there will be a nutritive layer of substrate to support plant growth, but it won’t overwhelm the water column.

After all, time is a limiting factor when doing a complete tank reset.

Remove and Clean Hardscape

Hardcape elements such as rock, driftwood, and other decorations are easy to store but not always easy to clean.

Hydrogen peroxide is the safest chemical to use and so is boiling water.

Mechanical cleaning — brush or another scrub — works well on driftwood and rocks alike. Cleaning thoroughly things like lava rock takes some time but even old stones can recover their vibrancy with a proper cleaning.

What’s more, mechanical and chemical cleaning will take care of parasites, algae, and illnesses.

Just don’t soak driftwood or porous rocks in vinegar or bleach as it may absorb them and poison your fish later on.

Low-concentration solutions of hydrogen peroxide are safe because it is a compound that dissolves harmlessly in water.

Keep the Filter

Unless you have a really good reason for sterilizing the filter, you shouldn’t even wash it during the tank reset. Filters are crucial for the microbial fauna of a fish tank and that will help the new setup to get established quickly.

Keep the filter in the hospital tank where your livestock is. The moment the new setup is complete, plug it in there so that it can start cycling the new aquarium right away.

It would be safe to clean the filter after 3-4 weeks have passed.

In case you are dealing with a disease and don’t want to risk it, then the new setup should undergo a complete nitrogen cycling that takes at least two weeks. Delicate plants may not survive that long.

Also, the fish should be kept in adequately sized vessel if possible, as 14 days or more cramped together will likely elevate their levels of stress.

Clean the Tank

Once the fish tank is empty, make sure to clean it well.

Hydrogen peroxide is best suited for the purpose but vinegar and salt also have a strong disinfecting effect and are easy to wash out.

Inspect the silicone seals of glass tanks and check acrylic tanks for scratches. They can be fixed, to an extent.

Managing the New Tank Setup

By bringing the filter from the old tank an aquarium can be safely restarted within a week.

However, if you are adding new active substrates like aquasoil or topsoil, you must perform regular water changes. To speed things up, daily changes of 20%-25% should be enough to make the water liveable within a week.

However, avoid planting the first couple of days. Then add first the sturdiest plants to see how they react. If there is no melting, add more sensitive species, too. It is best to add a plant or two from a given species and wait one day to see how it handles it before planting more.

Make sure to test for ammonia and nitrates before adding fish and shrimp.

Plan the Tank Reset in Advance

Performing a successful tank reset takes a few days and involves several processes. Grab a pen and paper and write down what you will do, and in what order.

Find storage places for the plants and set up a tank or bucket for the livestock.

Prepare cleaning materials — buckets, scrubs, hydrogen peroxide, etc. — for the substrate and hardscape elements.

Free up time on your calendar, as taking everything out of a tank, even if it isn’t overly big, is a time-consuming operation.

Tank resets are not the easiest thing to do, but they are a great learning opportunity. You will be able to take a very close look at the state of each element of the aquarium (and the tank itself!). It is very informative about how things have evolved since the initial setup.

Good luck and send pictures of the newly restarted tanks!