How many fish can I have in my aquarium?

Question

I have a 30 litre cold freshwater tank and I currently have four fancy goldfish (fantail orandas), one small catfish, six zebra danios and two yellow platys. Can I add a couple of guppies as well, or have I reached the maximum amount of fish that it is safe and healthy to keep in my aquarium?

There is visually a lot of space in the aquarium - it certainly isn't 'more fish than water' - they are all pretty small fish!

Dimensions wise, the aquarium is about 55cm wide, 45cm tall and the depth varies as it has a curved front (this is from memory - I'm sitting at my computer at work and the aquarium is at home, I think I am being conservative in my estimates and it's bigger than that).

How do you tell what the limit is? The water is well aerated - there is a good filtre plus a fair amount of low level plants (they don't take up much space) to create oxygen.

Great - thanks for that Hypocrite! It says I still have a little bit of space (tank has large surface area due to curved front) but I think I should save it for the potential growth of the fish...

I did do research and was informed by many websites that danios are fine in cold water, as are platys etc. I also asked in several aquatic shops before buying my goldfish as to what size tank I would need and bought a bigger tank than was suggested - I don't know anyone who has a 180 litre tank for goldfish! I was advised by the aquatic shops that goldfish will only grow very large if they have the space - i.e. they will grow very large in a large pond, and not in a tank. I always asked advice before buying the fish I have as to whether they were compatible etc and I was advised that they were, otherwise I wouldn't have bought them.

Kylie Anne, I resent your implication that I am irresponsible - as mentioned above, I HAVE always researched the compatibility of my fish before buying them. My catfish is not a corydora and I was advised that it was fine to get just one.

I definitely disagree with the fact that danios can only be kept in tropical conditions - I have had them for a year and they are happy and healthy. They have grown well and they are not feeling cold. Cold fish are sluggish and not interested in food. Mine are very active and very enthusiastic about their food. Yes, they are techinically tropical fish but I have a tropical fish breeding book which says many tropical fish are happy in cold water (at room temperature).

Besides, my goldfish are laying eggs which I am told is extremely unusual in private aquarium situations and means that they are content in their surroundings.

We have had common garden goldfish kept in a pond six feet deep that didn't grow to a foot in length in ten years, so I must say I am sceptical about my tiny fish growing that large - they have grown about 2cm in a year, and I am told my a friend who runs an aquatic shop that this is average growth.

I change 30% - 50% of the water in the tank once per week, as I was advised that this is necessary for goldfish as they create a lot of nitrates. I clean the filter regularly (at least once a month as recommended on the filter's operating instructions).

For those of you who are insisting that my danios are tropical only fish - please google 'coldwater danios' - it will bring up scores of websites that tell you that zebra danios (which mine are) among other types - are perfectly happy in cold water. As are mine.

Answer 1

It's not just the volume that dictates the number of fish you can keep. It is more dictated by the surface area. Oxygen can only be exchanged at the surface and if there isn't enough, then the fish would suffocate. The number is decided from the size of the fish too.
I found the Table below. It looks sensible.

Answer 2

You say that you did research but that is very hard to believe when you not only have a very overstocked tank with fish that don't belong together but you ask if you can add more, if you did do research then you would know the answer is no and you are putting all your fish at risk of a very unfortunate death. Having just one of those goldfish in the tank is overstocked enough, having 4 in there is just cruel then on top of that you have tropicals mixed in too. Every person that has answered you can't be wrong so maybe you should try that research thing again and find out what your fish really need to be happy, healthy and thriving. The sites that Kylie Anne listed are a good start.

Answer 3

Register with www.thinkfish.co.uk and go onto their community creator. You input the dimensions of your tank, filtration type etc. and then look up each individual fish and add that to the creator. It then tells you if you're overstocked or not as well as if there are any problem areas that need to be identified.

Going on personal experience, you have WAY too many fish for your aquarium and why do you keep tropical fish in with coldwater fish? Your tank is way too small for the goldfish. It should be at least 120 litres as it is a very common misconception that goldfish only grow to the size of the tank. They physically stop growing outwardly but their internal organs don't.

Answer 4

I would not put any more in as the more fish you have,the more waste is produced which then causes ammonia and all sorts of other unwanted results.Each fish needs room for growth so the more room they have the better it is.If you want to keep the tank in tip top condition not only water changes should be carried out but water testing too for nitrite,ammonia and ph levels etc.Water changes can help many situations but does not always give you the positive result you want.If it was me i would not put any more in.Them fancy goldfish can get really big.Sorry i cant be of much help but hope the advice i have left is helpful.

Answer 5

I know I am gonna get "hammered" by purist but I think there should be a better method of judging how many fishes can particular tank can take.

What I propose is a paradim shift from a fish per volume base to a nitrate removal base guage.

I have a write up here that explain what I believe, in the write up I use goldfishes as examples but it's the same for all fishes. This is based on experience, knowledge from books and internet, discussion groups and also base on some expriement done on keeping trouts in a barrel conducted by some others.

The conclusion for this question of how many fishes you can keep in a tank depends on the frequency and amount of water you're willing to change.

http://www.arofanatics.com/members/dragonfly_sg/howmanygoldfish/

Hope this helps.

Answer 6

PLEASE at least DO NOT get any more fish.

goldfish need 80litres to themselves when full grown. the goldfish you have can grow to be a foot long.

the danios are TROPICAL fish and need a heater, goldfish can't have heaters. these fish are NOT compatible.

most catfish are schooling fish, you should not have just one. depending on what kind it is it's also most likely in need of a heater. however, depending on what type of fish you actually have it may get huge. "sucker fish" get very very big, however corydoras only get 2-3 inches.

PLEASE take the goldfish back to a pet store or else get a 120litre tank for them. after you remove the goldfish get a heater and keep it at about 75F. then, if your catfish is a corydora get one or two more for company for it, that would be the MAXIMUM amount of fish to keep, and even that is pushing it.

from now on please do research BEFORE you get the fish.

*edit*
I did not mean to offend you, but you obviously did not do much research because both danios and platies are tropical fish that need heaters, also goldfish should not be kept with much of anything except goldfish. most pet stores don't care much about the welfare of the fish so much as making money. you can't keep those goldfish in that small of a tank, it is unhealthy. do a quick google search for the type of goldfish you have (and any goldfish really) and you will see they DO need that much space. just because many people don't provide their fish with this much room does not mean it is not the best conditions for the fish, it also does not mean keeping 4 goldfish that can grow to be a foot each in 8gallons of water is not cruelty. yes, they won't grow big if you keep them in small spaces but this shortens their life and causes malformations on the inside with things like the backbone. this can cause very serious and painful conditions for the fish... not to mention the serious ammonia poisoning that will happen.

I also advise you do a google search for danios and platies, you will find that they are tropical fish that need tropical temps.

searches on the internet and through books are proper research, relying on the people selling you things is not. it's like expecting mechanics to not throw in extras for more money to someone who knows nothing about cars.

although you'll assume I found ones with the info backing me up and won't believe em anyway i'm listing a few site with good information, if you don't trust them do your own search.
http://www.kokosgoldfish.com/ORANDAM.html
http://www.bristol-aquarists.org.uk/goldfish/info/keeping-fs.htm
http://www.kokosgoldfish.com/care.html

compatibility:
http://badmanstropicalfish.com/profiles/profile4.html
http://www.fishtanksandponds.info/live-stock/coldwater/tankmates-for-goldfish.htm

as I said before you're tank is really too small for goldfish and your best bet would be to get a heater and make it a tropical community tank.

Answer 7

You are pretty much maxed out there hun. Actually you are over loaded. Remember, 1" of fish for every 1 gallon of water. You may have to keep your eye on the PH and nitrate levels in your tank. If they all seem health, keep doing what you are doing just remember most aquarium disease is allowed to affect your fish because they are stressed. Stress from poor water conditions and overcrowding can weaken your fishes defenses and cause him to become more susceptible to the micro organisms typically present in the aquarium water which can then take hold and infect him with disease.

Answer 8

The average is 1 1/2 inches of fish per gallon for freshwater and 1 inch of fish for saltwater. Keep in mind when you put small fish in that they will probably grow.

Answer 9

The general rule is one inch of fish per gallon of water. However, goldfish are the dirtiest fish around, so the rule with them is one goldfish per ten gallons. I worked in a fish store.

Answer 10

30 litres is not much, it already seems like you have got a lot in there, basically there is more FISH than WATER just about.

Unless it is fish soup you are making, I'd say you already have enough.