Cardinal Tetras & Discus

[Oli]

Looking to clear out my cichlid tank and start again with a Discus and Cardinal tetra tank. It is approx 55 gallons and I will be purchasing 4/5 Discus. However in the mean time I will be looking to stock it with Cardinal tetras only while I save money for the discus. What’s the maximum number of tetras you would add, considering it will also have Discus in a couple months time?

 

[Byron]

Cardinal tetras (Paracheirodon axelrodi)...no fewer than 12, I would aim for 15 here. Plants to provide good cover, or branches (works for discus too), and definitely floating plants. This species has what Baensch called a light phobia--they do not like overhead lighting so floating plants help a lot.

On the discus, five is the absolute minimum, but six or seven would be better. Get the group at the same time, and at the same size. Many recommend purchasing only from a breeder, store discus at least in NA can be very risky. May be different in the UK.

 

[Oli]

Hi Byron, thanks for the response. So 15 Cardinal tetras followed by 5 discus at a later date would be okay for a 55 gallon? My store has absolutely incredible specimens that are fully grown, from what I see they look great. The guy advised getting them around the 5” mark and letting them all grow together. They do have large discus for around £100 each but the smaller ones (4/5/6”) are 2 for £55. I plan on rehoming my whole tank and adding 15 cardinals for the time being. Once I have some more time/money on my hands, I would then switch the substrate to sand and do some research on my plants and whether or not they can withstand the heat. Then add the 5 discus at the same time. Picture included for reference of tank

 

[Byron]

I see nothing wrong with that aquascape for discus and cardinals, except one thing...floating plants. Essential for both fish under consideration.

Not sure why you want to change the substrate, but that's up to you. Big job.

I'll leave it for the discus experts to comment, but 5-inch discus seem quite large. Symphysodon aequifasciatus attain six inches, S. discus attain 8 inches at maturity.

 

[Oli]

Great, I’ll be sure to get some suitable floating plants!

Regarding the substrate I was advised that sand was the best option due to it showing any waste clearly so it is easier to clean. Also the waste should remain on the surface as opposed to falling between the bits of gravel, again making it easier to clean and keep all parameters perfect. I understand they are very sensitive fish.

Perhaps I was overestimating a bit there! The largest ones were certainly pushing towards 8”. Perhaps more like 4” were the advised size to get.

Thanks for the help

 

[threecharacters]

I see nothing wrong with that aquascape for discus and cardinals, except one thing...floating plants. Essential for both fish under consideration.

Not sure why you want to change the substrate, but that's up to you. Big job.

I'll leave it for the discus experts to comment, but 5-inch discus seem quite large. Symphysodon aequifasciatus attain six inches, S. discus attain 8 inches at maturity.

Great, I’ll be sure to get some suitable floating plants!

Regarding the substrate I was advised that sand was the best option due to it showing any waste clearly so it is easier to clean. Also the waste should remain on the surface as opposed to falling between the bits of gravel, again making it easier to clean and keep all parameters perfect. I understand they are very sensitive fish.

Perhaps I was overestimating a bit there! The largest ones were certainly pushing towards 8”. Perhaps more like 4” were the advised size to get.

Thanks for the help

With regards to size, I was reading up on discus husbandry recently and captive bred discus can end up significantly larger than wild specimens (9-10" is possible for captive bred discus). Discus breeders obsess over maximizing growth. Many employ a crazy water change schedule (daily or every other day) along with overfeeding while the discus are still juveniles. Their goal is basically to grow the discus to sellable size in as short a time as possible. As a result, they end up with "roided" out discus that can grow to nearly twice the size of wild individuals.

 

[Oli]

While I’m sure I know peoples answer to this question, I am wandering if it would be possible to get just 2 of the large discus along with a load of cardinals, as opposed to 5 medium discus. Would this be likely to stress them? I know they like to be in groups, but would having 2 with more space outweigh that? Again I am not rushing into this and keen to hear a range of opinions, thanks

 

[Byron]

While I’m sure I know peoples answer to this question, I am wandering if it would be possible to get just 2 of the large discus along with a load of cardinals, as opposed to 5 medium discus. Would this be likely to stress them? I know they like to be in groups, but would having 2 with more space outweigh that? Again I am not rushing into this and keen to hear a range of opinions, thanks

This is not advisable, unless you can acquire a bonded mated pair. Discus are very similar to angelfish in this respect. They are shoaling fish that live in groups. They develop an hierarchy within a group placed in the aquarium, and having two, three or usually four rarely works because of their temperament. There are always exceptions, but it is better to assume the fish we acquire will be normal and not abnormal. A group of five or more should spread out any dominance, though again there are always the exception. Eventually a male/female pair may form, and then you are in another situation. Discus are generally not as rough as angelfish, but they are still cichlids and territory and dominance can be very strong.

On the size, Jack Wattley used to advise purchasing discus together at the 3 inch or maybe it was 4 inch size, to have better luck establishing the group hierarchy. No one knew more about discus than he did.

Another thing, if you did luck out with two or three "compatible" discus, adding a fourth and fifth later is really asking for trouble.

 

[Byron]

Great, I’ll be sure to get some suitable floating plants!

Regarding the substrate I was advised that sand was the best option due to it showing any waste clearly so it is easier to clean. Also the waste should remain on the surface as opposed to falling between the bits of gravel, again making it easier to clean and keep all parameters perfect. I understand they are very sensitive fish.

Perhaps I was overestimating a bit there! The largest ones were certainly pushing towards 8”. Perhaps more like 4” were the advised size to get.

Thanks for the help

Sand is overall a better substrate, I agree. Some fish need sand, but discus and cardinals are not in that situation, and cories or loaches for example are out of the question here due to warmth (cories) or activity/temperament (loaches). But yes, I concur that sand if not black or white can be more aesthetically pleasing. And it is less likely of bacterial issues.

 

[Oli]

This is not advisable, unless you can acquire a bonded mated pair. Discus are very similar to angelfish in this respect. They are shoaling fish that live in groups. They develop an hierarchy within a group placed in the aquarium, and having two, three or usually four rarely works because of their temperament. There are always exceptions, but it is better to assume the fish we acquire will be normal and not abnormal. A group of five or more should spread out any dominance, though again there are always the exception. Eventually a male/female pair may form, and then you are in another situation. Discus are generally not as rough as angelfish, but they are still cichlids and territory and dominance can be very strong.

On the size, Jack Wattley used to advise purchasing discus together at the 3 inch or maybe it was 4 inch size, to have better luck establishing the group hierarchy. No one knew more about discus than he did.

Another thing, if you did luck out with two or three "compatible" discus, adding a fourth and fifth later is really asking for trouble.

Ahhh okay and how about a singular adult discus? Would it be stressed out being alone? Perhaps 5 medium sized is the way to go

 

[Byron]

Ahhh okay and how about a singular adult discus? Would it be stressed out being alone? Perhaps 5 medium sized is the way to go

I would never put a lone discus in a tank, that is inhumane. This is a shoaling fish; the expectation of being in a group is programmed into the genetic coding of the species. This is why it is so critical to understand the habitat of a fish species. If we expect healthy fish, we must avoid as much stress as possible. Forcing a lone discus to live in isolation is not going to avoid stress, quite the opposite. There has been more than one study over the last decade that determined clear scientific evidence that this is the case. Shoaling fish denied a group have increased aggression, are more prone to dart when startled, and even show a latency to feed compared to fish of the species maintained in groups. Given these negatives, there can be no doubt how serious this is for the well being of the fish.

 

[Oli]

Cool, that’s why we do our research looks like I will plan on five, 4” discus with around 15 cardinals. I will be sure to do a lot more research and visits to the LFS and also have a good think about substrates! Thanks for the help

 

[itiwhetu]

I don't think 55g is large enough for Discus, especially five. My pair was housed in a 250 liter tank with Cardinals.