Assorted Corydoras Mix

Choose the mix for flexible community planning

The Assorted Corydoras Mix, Corydoras sp. (mixed), is a mixed assortment of Corydoras catfish in the family Callichthyidae. These are social freshwater catfish for the lower part of a community aquarium. They suit a keeper who can maintain a mature, filtered tank, feed the fish directly at the bottom and plan around an assortment rather than one named species.

Keep at least five together and use an aquarium of at least 80 litres as the starting point for a shoal of smaller catfish such as Corydoras. Keep the water at 22–26°C, pH 6.0–7.5 and 4–15°dH, with ammonia and nitrite at 0 mg/l. Larger fish would require more space, so treat 80 litres as a starting point rather than a universal final aquarium.

The assortment format makes flexibility important. If your aquarium has a tightly defined temperature, a fixed adult-size limit or a species-pure social group, a named Corydoras gives you a clearer long-term plan.

Understand the fish and size supplied

One purchase supplies one live fish from the selected size. Use the live size selector to choose 2.5–3 cm, 3–3.5 cm or XL. The 2.5–3 cm and 3–3.5 cm options are dispatch sizes, and XL is a dispatch grade with no centimetre figure.

The size you select is the size supplied, not the adult size. Adult size depends on which Corydoras is included in the assortment. Do not use a dispatch grade to decide whether the mature fish will fit your aquarium. Instead, start with the OATA planning figure of at least 80 litres for a shoal of smaller catfish such as Corydoras and allow more room when the individual fish requires it.

What the mixed identity means

Fish in this assortment can be different Corydoras species rather than one named species. Colour, pattern and adult size can differ between fish in this assortment. Choose this mix when those differences fit your plans; choose a named Corydoras when an exact identity, fixed adult size or narrowly defined temperature requirement is essential.

Sex is guaranteed only when the selected option explicitly states male or female. This Assorted Corydoras Mix listing has no sex-guaranteed option.

The gallery images are representative of this type of animal rather than photographs of the exact animal supplied, so colours can look slightly different from the live animal.

Decide whether an assortment fits your goal

Choose the assortment when

• You want Corydoras for a peaceful freshwater community and can maintain a group of at least five.
• Your aquarium can operate within 22–26°C, pH 6.0–7.5 and 4–15°dH.
• You can provide at least 80 litres for a shoal of smaller catfish such as Corydoras and increase the space if the fish’s eventual requirements call for it.
• You are comfortable with natural variation in pattern and final size across the assortment.

Choose a named Corydoras when

• You need a fixed adult-size figure before planning the aquarium.
• You are building a species-pure group or a breeding project.
• Your other livestock requires a narrow temperature or water-chemistry range.
• You want several fish with the same named identity rather than a mixed selection.

You can compare named fish in the Corydoras collection. Match the named animal’s adult size, social needs and water range to the aquarium before choosing it.

Whichever route you take, prepare the aquarium before the fish arrives. A mature biological filter, stable temperature, 0 mg/l ammonia, 0 mg/l nitrite and a deliberate feeding place at the bottom are practical essentials for this mix.

Prepare a mature aquarium with safe cover

Prepare a mature, filtered aquarium before introducing the fish. OATA recommends an aquarium of at least 80 litres for a shoal of smaller catfish species such as Corydoras, while much larger aquariums are needed for bigger species. An assortment should therefore begin with that smaller-fish planning figure, not end with it. Choose as large an aquarium as practical, because a larger volume keeps temperature and water quality more stable.

If this is your first aquarium, follow our guide to preparing and maturing a first tropical tank before livestock arrives. Maturing the filter allows the beneficial bacterial population to process fish waste. Adding fish before that population is ready can allow toxic ammonia and nitrite to rise.

Build the lower area around the fish

• Substrate: use fine sand or very smooth rounded gravel. Corydoras search along the bottom with their barbels, so avoid sharp or abrasive material.
• Cover: provide live plants where practical, with wood, pots, caves or suitable ornaments creating sheltered areas.
• Feeding access: leave an open area where sinking food can land and where every fish can reach it.
• Filtration: use a well-set-up biological filter and check that it continues to move and clean the water effectively.

Arrange the aquarium so that shelter does not consume the whole feeding area. A useful layout has planted or furnished edges, one or more covered resting places and a clear patch of smooth substrate for meals. Watch where the fish gather when food reaches the bottom; if one shelter or ornament blocks access, move the feeding point rather than increasing the portion.

Introduce livestock gradually. Each additional fish and each extra meal increases the work required from the filter bacteria. Slow stocking gives that bacterial population time to grow and reduces the risk of new tank syndrome.

Complete a readiness check

Make the final decision from measurements and usable space, not the aquarium’s appearance. Confirm that the filter is running normally, ammonia and nitrite both read 0 mg/l, the temperature is stable within 22–26°C and the planned Corydoras group has an accessible feeding area. An aquarium can look established while its biological filter is not ready for a larger waste load.

Check the arrangement from the fish’s level before adding livestock. Food should be able to reach smooth substrate without disappearing beneath inaccessible ornaments, and covered areas should not trap waste where it cannot be siphoned. If the only open area lies in a busy feeding route used by faster fish, prepare a second feeding point before the Corydoras arrive.

Hold the water within the catfish range

Keep the aquarium at 22–26°C, pH 6.0–7.5 and 4–15°dH. Hold ammonia and nitrite at 0 mg/l, and keep nitrate from rising more than 20 mg/l above the normal tap-water level. Stability within these limits is more useful than repeatedly adjusting the aquarium towards one edge of the range.

Measure the aquarium rather than relying on how clear the water looks. Our water-chemistry guide explains what the principal readings mean, while the water matcher helps compare your measured values with the stated range. Record the temperature, pH, hardness, ammonia, nitrite and nitrate so that a change can be seen rather than guessed.

Give the filter the central role

The RSPCA explains how biological filtration supports fish welfare: fish release toxic ammonia, bacteria convert it to nitrite, and another bacterial stage converts nitrite into the safer nitrate. That process depends on a well-set-up and maintained filter. Clear water can still contain dissolved ammonia or nitrite, so testing remains essential.

Do not solve a poor test result by adding more fish, more food or several rapid chemical adjustments. First confirm the reading, inspect the filter and review the recent stocking and feeding load. Prompt, measured action protects both the fish and the biological filter.

Work from the tap-water baseline

The nitrate limit is measured against the normal tap-water level, not against zero. For example, if conditioned tap water reads 10 mg/l nitrate, keep the aquarium from exceeding 30 mg/l under OATA’s limit of no more than 20 mg/l above that baseline. If the tap-water reading changes, update the comparison rather than continuing to use an old number.

Use trends to decide when routine needs attention. A single reading records one moment; several readings taken with the same method show whether nitrate is accumulating faster or pH is moving. When a result changes unexpectedly, repeat the test before altering the aquarium, then compare it with recent feeding, stocking and filter-flow observations.

Use a repeatable weekly maintenance routine

Complete a partial water change of 25% at least once a week. Use a siphon to remove solid waste from the substrate, especially around feeding areas and beneath accessible ornaments. Treat replacement tap water with a suitable conditioner before it enters the aquarium so chlorine or chloramine does not harm the fish or filter bacteria.

Use the weekly change as a complete check

1. Test ammonia and nitrite and confirm both remain at 0 mg/l.
2. Check nitrate against the aquarium’s normal post-change baseline and the OATA limit.
3. Measure temperature and pH before making any adjustment.
4. Siphon visible waste while removing about one quarter of the water.
5. Condition the replacement water before adding it.
6. Inspect the filter for a blocked intake, reduced flow or trapped debris.
7. Observe the fish after the change for normal breathing, swimming and feeding.

If the filter media needs cleaning, rinse it lightly in aquarium water removed during the water change. Do not rinse established biological media under the tap because chlorine or chloramine may kill beneficial bacteria. Avoid replacing all mature filter media at the same time.

Changing 25% of the water at least once a week does not mean waiting for the weekly change when a test reveals a problem. If ammonia or nitrite rises above 0 mg/l, respond to the measured condition promptly and investigate the cause. Recent additions, excess food, decaying material or restricted filter flow can all increase the waste burden, so review what changed immediately before the reading moved.

Keep the routine consistent

Use the same test method and broadly similar point in the maintenance cycle each week. Comparable readings show whether nitrate is accumulating faster, pH is drifting or filter performance is changing. Write down unusual behaviour alongside the numbers; the combination often gives a clearer warning than either observation alone.

Translate the percentage into a practical amount

For an 80-litre aquarium, 25% is 20 litres. Marking that amount on a dedicated container makes the weekly change repeatable and prevents a rough estimate from becoming much smaller over time. For a different aquarium volume, multiply the volume by 0.25 to find the weekly amount before displacement by substrate and furnishings.

Use the siphon deliberately rather than disturbing every area at once. Start with places where sinking food lands and where visible debris gathers, then inspect around accessible shelters. The aim is to remove accumulated solid waste while preserving the established biological filter. Keep removed aquarium water aside when filter media needs its light rinse, then discard it after that task.

Finish by checking that the filter intake is clear and flow has returned to its normal level. Record the post-maintenance readings so next week’s values have a useful comparison point. If the fish behave differently after maintenance, compare temperature and pH with the pre-change readings before making another change.

Feed the bottom dwellers directly

Feed an appropriate sinking food once a day, offering only what the fish can eat within a few minutes. OATA identifies Corydoras as omnivorous catfish and warns that catfish should not be expected to live as scavengers. Food must reach the lower part of the aquarium in a form the group can find and eat.

Sinking pellets or granules provide a practical main food. Suitable frozen or live foods such as daphnia, Artemia or bloodworm can add variety where appropriate. Introduce variety in controlled portions and remove uneaten food rather than allowing it to break down in the substrate.

Make sure every fish gets a share

• Place food in the open area of smooth substrate prepared for feeding.
• Watch the first few minutes rather than assuming food reaching the bottom has been eaten.
• If faster midwater fish intercept everything, divide the portion between two locations or adjust the feeding method.
• If one Corydoras repeatedly misses the meal, check whether cover, competition or the food size is preventing access.
• Reduce the next portion if food remains after the feeding period.

Do not increase the portion simply because the fish continue to search the substrate. Searching is not a measured feeding amount. Judge the meal by whether each fish eats, whether food remains after a few minutes and whether body condition stays steady.

Overfeeding is a water-quality problem as well as a diet problem. Uneaten food decomposes and adds waste that the biological filter must process. A small observed meal is safer than an oversized portion hidden among plants or gravel.

Calibrate the meal by observation

Begin with a controlled portion at the prepared feeding point and watch the whole feeding period. The correct amount is the amount the group consumes within a few minutes, not a fixed number of pellets for every aquarium. Food size, the number of fish and competition from other inhabitants all affect whether the meal actually reaches each Corydoras.

Use two feeding points only when that solves a visible access problem. Place both where you can see the food and remove anything left behind. If food disappears into deep gravel, beneath wood or behind an ornament, change the landing place before adding more. This keeps the feeding decision separate from the temptation to compensate with a larger portion.

Review appetite alongside the water test results. A group that suddenly loses interest in the usual meal needs an immediate water-quality check. If appetite remains normal but one fish repeatedly misses food, focus on access, competition and the position of the feeding area.

Follow the arrival sequence in order

Be present to receive the parcel and inspect it on the day it arrives. Start filming before the parcel is opened. Record one continuous take showing the sealed parcel with the outer box visible, the parcel being opened and the fish still inside the sealed bag.

Follow the Tropical Fish Co delivery and Live Arrival Guarantee policy: float the bag for 20–30 minutes before releasing the fish, and do not pour the bag water into the aquarium. Contact us on the same day with the order number and the short continuous unboxing video if a claim is required.

Check the aquarium before release

Confirm that the aquarium is ready for livestock. Temperature should be within 22–26°C, ammonia and nitrite should both read 0 mg/l, and the filter should be operating normally. Do not use the arrival of the fish as the point at which the aquarium is first tested.

1. Before opening: begin the continuous video.
2. On opening: keep the fish inside the sealed bag while its condition is recorded.
3. Before release: float the bag for 20–30 minutes.
4. At release: transfer the fish without pouring transport water into the aquarium.
5. After release: observe breathing, balance and swimming without adding more livestock.

OATA advises increasing the aquarium population slowly because the filter’s beneficial bacteria must respond to the extra waste and feeding. Even a mature filter has a working capacity, so space additions rather than treating one successful introduction as permission to add a large number of fish immediately.

Prepare the measurements before the parcel opens

Write down the aquarium temperature, pH, ammonia and nitrite readings before starting the arrival process. This prevents the fish’s arrival from becoming the first point at which a filter or water problem is discovered. If ammonia or nitrite is above 0 mg/l, the aquarium needs attention before livestock is released into it.

Use feeding and behaviour as early checks

Use each daily meal as a short health check. Healthy fish should show appropriate swimming behaviour, clear bright eyes, intact scales and fins, normal breathing and an interest in food. Learn the group’s normal appearance and behaviour so that a darker or paler colour, increased hiding or a change in swimming can be recognised quickly.

Respond to changes with measurements first

A change in behaviour does not identify one cause by itself. Testing separates a water-quality emergency from feeding competition or a compatibility problem. Write down the result and the observed change before altering several parts of the aquarium at once.

Whenever you are concerned about a fish’s health, test the water and contact us for further guidance. Include the aquarium volume, temperature, pH, ammonia, nitrite, nitrate, recent additions and maintenance history. Those details make the next decision more precise.

Protect the group through steady routines

Continue daily feeding observation, weekly testing and a 25% water change at least once a week. Do not relax the routine because the water looks clear. Dissolved ammonia and nitrite cannot be judged by sight, while nitrate trends and gradual pH changes are easiest to manage when regular readings reveal them early.

Keep a short observation record

Record only details that help with the next decision: whether every fish reached food, whether breathing and swimming looked normal, and whether colour, hiding or body condition changed. Pair unusual observations with the measured temperature, pH, ammonia, nitrite and nitrate. A dated note shows whether a change was brief, repeated after feeding or followed recent stocking or maintenance.

Change one manageable factor at a time unless ammonia or nitrite requires prompt action. If a fish misses one meal because another fish blocks the feeding point, correct access and watch the next meal. If several fish lose interest together, test the water and inspect the filter before changing the food. Look at the whole group before choosing the first check, and do not treat behaviour alone as a diagnosis.

Build a social group with enough space

Keep at least five Corydoras together. OATA warns that Corydoras kept singly or in groups that are too small will often become stressed. Count the group before assessing decorative space or adding unrelated bottom-dwelling fish; the Corydoras social requirement comes first.

A mixed selection does not replace a group of the same Corydoras species. The best group is several of one species or a clearly compatible close group; use a named, species-pure group when exact identity is central to your goal. Do not rely on a mixed assortment as a matched breeding group.

Check the group against the aquarium

• Volume: use at least 80 litres for a shoal of smaller catfish such as Corydoras and provide more room if the fish requires it.
• Bottom access: leave enough smooth, open substrate for all fish to feed without crowding one point.
• Shelter: provide several covered areas rather than one space that every fish must share.
• Food: observe each fish eating instead of assuming one group portion reaches everyone.
• Water: keep the aquarium at 22–26°C, pH 6.0–7.5 and 4–15°dH.

If the aquarium cannot hold at least five with suitable floor space, shelter and stable water quality, choose a different stocking plan. Reducing the group below five is not a substitute for providing enough room.

Additions should be gradual. Test ammonia and nitrite before increasing the group, then continue the usual weekly checks. A sudden rise above 0 mg/l indicates that the biological filter and waste load need attention before any further fish are introduced.

Plan the whole group before the first addition

A minimum group of five is a stocking commitment, not a reason to add fish faster than the biological filter can support. Decide how the full group fits the aquarium, then pace introductions according to filter maturity and measured ammonia and nitrite. Both readings must remain at 0 mg/l before the stocking plan moves forward.

Recheck access when the group grows. A feeding place that works for one or two fish may become crowded when at least five use it, while a single shelter may not give the whole group practical cover. Add another visible feeding point or rearrange suitable cover when observation shows restricted access; do not solve crowding by reducing the Corydoras group below OATA’s minimum.

Screen every community tank mate

Pair the mix with peaceful community fish whose temperature, pH and hardness needs overlap. OATA identifies Corydoras as suitable community-aquarium catfish, but catfish compatibility varies widely across the wider group. Screen the actual aquarium rather than relying on the word “community” alone.

Use four checks before combining fish

1. Water overlap: every animal must be able to live at 22–26°C, pH 6.0–7.5 and the chosen hardness within 4–15°dH.
2. Behaviour: avoid aggressive bottom dwellers and large predatory fish.
3. Feeding access: make sure faster fish do not take all sinking food before it reaches the Corydoras.
4. Space: retain enough lower-area shelter and open substrate for a group of at least five.

Do not add a proposed companion when only one check works. A peaceful fish with incompatible water needs is still a poor match, while a fish sharing the same temperature can still create persistent feeding or bottom-space competition.

Monitor fins, breathing, hiding and feeding after any introduction. If one fish is repeatedly chased, excluded from food or damaged, act on the observed conflict rather than waiting for the weekly maintenance day. For a stocking and compatibility assessment, ask us with the aquarium volume, dimensions, measured water values and full livestock list.

Work through a proposed match

Start with the companion’s required range. If it cannot remain at 22–26°C, pH 6.0–7.5 and the chosen point within 4–15°dH, stop there. If the water overlaps, assess behaviour next, followed by lower-area space and whether sinking food can reach the Corydoras.

A proposed companion passes only when all four checks work together. For example, a peaceful fish with overlapping water may still be unsuitable if it prevents the group from reaching food. Change the feeding arrangement and observe the result before treating the combination as workable. Repeated chasing, fin damage or exclusion from food is a failed compatibility outcome even when the test readings remain within range.

Repeat the screen whenever the community changes. Adding another fish alters the waste load, use of shelter and competition at feeding time. Check ammonia and nitrite after introductions and pause further additions if either rises above 0 mg/l.

Get clear answers before choosing the mix

What size of Assorted Corydoras Mix will I receive?

Choose 2.5–3 cm, 3–3.5 cm or XL from the live size selector. Your selected size is the supplied dispatch size rather than an adult-size figure.

What size aquarium does the Assorted Corydoras Mix need?

Use at least 80 litres as OATA’s planning figure for a shoal of smaller catfish such as Corydoras. Larger fish need more space, so choose a named fish when you require one fixed minimum aquarium size.

How many Assorted Corydoras Mix catfish should I keep together?

Keep at least five together, ideally as several of the same Corydoras species or a clearly compatible close group. OATA advises that Corydoras are shoaling fish and that individuals kept alone or in groups that are too small will often become stressed; a mixed selection does not replace a group of one species.

Does this fish suit a beginner?

It suits a keeper who can run a mature filtered aquarium, test the water every week, complete a 25% water change at least once a week and plan around a mixed identity. Choose a named Corydoras if you need fixed adult-size and temperature details.

What does the Assorted Corydoras Mix eat?

Feed suitable sinking pellets or granules once a day, giving only what the fish can eat within a few minutes. Corydoras are omnivorous, and suitable frozen or live foods such as daphnia, Artemia or bloodworm can add variety.

What temperature and pH does the Assorted Corydoras Mix need?

Keep it at 22–26°C, pH 6.0–7.5 and 4–15°dH. Maintain ammonia and nitrite at 0 mg/l and avoid sudden changes within the range.

Is the Assorted Corydoras Mix peaceful?

Corydoras are peaceful catfish suited to a community aquarium. Monitor fins and behaviour after introductions, and avoid aggressive bottom dwellers or large predatory fish.

Which kinds of animals can it live with?

It can potentially live with peaceful community fish whose water needs overlap. Check temperature, pH, hardness, bottom space and feeding access for every proposed companion rather than treating any species as a universal match.

How is this fish packed and delivered in the UK?

Fish are hand-bagged in pure oxygen, placed in an insulated poly box and given a heat pack when the weather calls for it, then carried by a licensed live-animal courier. Be present to receive the parcel, start a continuous unboxing video before opening, then float the bag for 20–30 minutes before releasing the fish.

Check the care and offer references

• OATA, How to look after freshwater catfish: water values, social group, aquarium planning, feeding, maintenance and health observations.
• RSPCA fish-environment guidance: biological filtration and aquarium waste processing.
• Tropical Fish Co delivery and Live Arrival Guarantee policy: packing, receipt, unboxing evidence and acclimatisation steps.