Overstocked cory tank?

Starsky · Post by **Starsky** » 27 Jun 2005, 03:17

I've recently gone into a cory shopping spree and i am afraid that i have overstocked my tank. I've read somewhere that the ideal load of an aquarium is an inch of fish to a gallon of water. I have a fifteen gallon tank and twenty-four cories (3 caudimaculatus, 10 panda, 3 sterbas, 2 schwartzis, 6 agasizii/leucomelas). I know that by the 1 inch to a gallon standard, I have miserably failed but because cories rarely move and hide in the caves all the time, my tank still looks scarcely populated.

Still, I don't want to sacrifice my cories' wellbeing for aesthetics. So, shall I get a bigger tank?

jedink · Post by **jedink** » 27 Jun 2005, 05:08

an inch per gallon may be a good rule of thumb, but sounds a bit conservative to me.....

Generally the stocking rate of a tank is dependant upon 3 things....the amount of filtration, aeration and how often and how much of your water you change.

if you have a decent filter with a good flow rate and maintain it well,and if you have plenty of aeration to keep the O2 levels up......also regular water changes are esential..i do about 25 % weekly

if you do all three of these you an heavily stock tanks without too many problems

jen.nelson · Post by **jen.nelson** » 27 Jun 2005, 05:28

The "inch per gallon" rule is really insufficient to determine stocking levels due to the complexity of what makes a tank overstocked - either not enough "inputs" available (such as oxygen, hiding places or other resources), or too many "outputs" (waste products of metabolism, for instance).

If you start to think about this, it's really complicated - beefier fish have more biomass than slender fish, so you'd expect that, per inch, they have more impact. But, type of diet (protein levels, volume of waste generated, etc) also plays a role - the higher the protein content and/or the higher the metabolic rate, the more nitrogenous wastes produced. Then, you have behavioral issues - a tank is more full (from a co-habitation standpoint) with 10 inches of fast-moving, agressive fish than with 10 inches of slow, placid fish. And the issues could go on...

In terms of waste products, I'd suggest monitoring nitrate levels before your regular water changes. I've read that if you can keep the nitrates below 20 ppm between your regularly scheduled changes, you're stocked OK. Obviously, the whether 20 ppm is really allowable is going to depend on the sensitivity of the fish you're keeping. In terms of behaviour, I think you just have to observe and learn and adapt... if your fish seem unhappy or bullied, etc, then you've got a stocking problem, no matter how many inches of fish you have.

Hope this is helpful rather than confusion-inducing....

As a side-note, I recently moved a group of ~6 cories from a relatively "more crowded" situation to a "less-crowded" tank in order to keep the tank cycled for me, and they seem less happy than when they were "crowded"... So, I'm going to fish-swap tomorrow... it's the learning part of this hobby that I enjoy the most...

Best,
Jen

MatsP · Post by **MatsP** » 27 Jun 2005, 10:20

Jenm

That's a good summary of things to consider when stocking...

jen.nelson wrote: In terms of waste products, I'd suggest monitoring nitrate levels before your regular water changes. I've read that if you can keep the nitrates below 20 ppm between your regularly scheduled changes, you're stocked OK. Obviously, the whether 20 ppm is really allowable is going to depend on the sensitivity of the fish you're keeping. In terms of behaviour, I think you just have to observe and learn and adapt... if your fish seem unhappy or bullied, etc, then you've got a stocking problem, no matter how many inches of fish you have.

Nitrate level of 20ppm "at the end of water change cycle" is a good level to be below for almost ALL fish, including sensitive species. Higher nitrate levels can be tolerated by many species, but can also cause problems with stunted growth and higher likelyhood of catching deceases.

Also, it's probably a better idea to increase the frequency of the water change than to increase the volume of the water changes if the water starts to accumulate nitrate (or other waste) too quickly. The main reason for this is that the difference between "low" and "high" nitrate levels will be smaller, and the average level will be lower...

--
Mats

Starsky · Post by **Starsky** » 27 Jun 2005, 13:26

I must admit that I haven't been checking nitrate levels yet but I will soon, thanks for the info, Jen. I have a bunch of plants in the tank so i'm banking on that to keep a bit of nitrate at bay.

I also do a 25-30% water change every week. And I do feel the one inch per gallon rule is a bit conservative, too, especially for corydoras. Thanks, jedink, for the comments. It's very comforting-- my corydoras look happy with their current school, it'd be a shame to break them apart.

MatsP · Post by **MatsP** » 27 Jun 2005, 14:46

Plants will take up nitrate to some extent, but there comes a point when the fish produce waste quicker than the plants can consume it.

Keeping an eye on the nitrate levels is a good way to know that you're doing the right amount of water changing, and perhaps adjusting the water change frequency/volume.

Obviously, it's most important to check the nitrate levels a couple of weeks after adding new fish, or if the fish grows quickly, you'll want to also do some extra checks. If the stocking stays neutral, i.e. fish doesn't grow much and you don't add or remove any fish, you can probably live with checking nitrate perhaps once a month on a regular basis.

Of course, there are also other waste than nitrate in the water, but it's fair to say that nitrate is easier to test for and can be used as a reasonable indicator of the overall water quality.

--
Mats

jedink · Post by **jedink** » 28 Jun 2005, 02:46

PS. while we are on the topic of stocking rates

i just completed a one year course in aquaculture, one of the things discussed briefly was the Extreme Density Units, these things can hold up to 1000 yabbies (Koonyacs, i think for our American friends) per Meter cubed ( 1000L, dunno in gallons)

they work by giving every yabby a "Cell" of its own. this eliminates;
-predation, by effectively taking the farm from the dam and moving it indoors
-cannibalism, no contact between the yabbies
-uncontrolled breeding.so the farmer can deliver a known amount, and also not have to overfeed to compensate for competition between juveniles and adults

so it is possible to have very high stocking rates...it just depends on how far you want to go, what resources you have on hand and what aesthetics you want. EDU's are not something i would put in my loungeroom to admire

bronzefry · Post by **bronzefry** » 28 Jun 2005, 15:12

Please correct me if I'm wrong, but isn't aquaculture something different from Cories in a tank in a person's home? I would think the two are very different. I'm not sure if you're referring to aquaculture in terms of a foodsource or for ornamental fish. Can you please enlighten me?

jedink · Post by **jedink** » 28 Jun 2005, 15:57

yeah aquaculture is different from a tank in a living room full of cories.....but the only real differences are scale and purpose..ie food instead of decoration.

all aquaculture is just maintaining aquaria from the size of your average fish tank to a farmers dam, the two are not that different..you breed fish, you grow them, you sell them, whether you sell them for food or decoration is probably the only real difference.

I was just trying to put across that stocking rates can be extreme if your water quality is optimal.

MatsP · Post by **MatsP** » 28 Jun 2005, 16:27

Yes, there's no doubt that you can stock quite a lot of fish in a tank if you have the right setup, including good filtration. You just have to look at some of the tanks in some fish shops that contain many more fish than you would normally keep at home, simply because the filtration system is much better in these shops than what you would use at home [the filtration is centralised and not "per tank"].

However, the example you give, Yabbies, a fresh-water crayfish, is not a good example of how to keep fish, because:
1. It doesn't necessarily need swiming space (1 liter of water per fish when they grow to about 160 mm wouldn't make sense for something that wants to swim).
2. According to this native australian fish site, the Yabbies are VERY tolerant to poor water quality, so the same stocking level for some fish that are less tolerant of poor water would require much higher level of filtration.

I certainly wouldn't want to try to keep that many fish per liter in my home aquarium.

btw, one US gallon = 3.8 liter -> 1000L = 263 us gal, one UK (Imperial) gallon = 4.5 liter -> 1000L = 222 imp gal.

--
Mats

bronzefry · Post by **bronzefry** » 29 Jun 2005, 14:42

Thanks for the info, folks! I just didn't know the difference.

Starsky · Post by **Starsky** » 03 Jul 2005, 17:10

MatsP wrote:Yes, there's no doubt that you can stock quite a lot of fish in a tank if you have the right setup, including good filtration. You just have to look at some of the tanks in some fish shops that contain many more fish than you would normally keep at home, simply because the filtration system is much better in these shops than what you would use at home [the filtration is centralised and not "per tank"].

However, the example you give, Yabbies, a fresh-water crayfish, is not a good example of how to keep fish, because:
1. It doesn't necessarily need swiming space (1 liter of water per fish when they grow to about 160 mm wouldn't make sense for something that wants to swim).
2. According to this native australian fish site, the Yabbies are VERY tolerant to poor water quality, so the same stocking level for some fish that are less tolerant of poor water would require much higher level of filtration.

I certainly wouldn't want to try to keep that many fish per liter in my home aquarium.

btw, one US gallon = 3.8 liter -> 1000L = 263 us gal, one UK (Imperial) gallon = 4.5 liter -> 1000L = 222 imp gal.

--
Mats

This is very informative. Thanks! Also, I've always wondered about those fish shops and their overpopulated tanks.

I just realized, an earlier topic had practically the same query as mine-- how many cory, by corrymad. In that topic, corybreed said: "Fourteen corys in a 15 gallon tank is too many! In my view 6-10 average size fish is enough. You might be able to get by with strong filtration and water changes but the tank will still be too crowded. If you stock the tank with pygmy corys 15-20 will be fine and would make nice presentation." If I'm not mistaken, this approximates the one inch of fish to a gallon of water rule.

I guess we have two popular schools of thought going on here.

jen.nelson · Post by **jen.nelson** » 03 Jul 2005, 18:28

This is very informative. Thanks! Also, I've always wondered about those fish shops and their overpopulated tanks.

I've also noticed in some shops that they appear to use an ammonia absorbant sponge/granular placed inside the filter box, in addition to having a very large filtration system.

I guess we have two popular schools of thought going on here.

Yup, as with so many things in life, there's not one right answer - there's lots of things that work for lots of people under lots of different circumstances. The nice thing here is that, for the most part, folks can discuss their different ideas without it becoming unfriendly.

I would add that, while this site is great for getting an idea of what works for other folks, there really is no substitute for observation - the fish will tell you what's going on by how they're acting, and it's important to be keyed into that...

Best,
Jen

racoll · Post by **racoll** » 03 Jul 2005, 18:55

i would say 24 cories in a 15G sounds like too many.

BUT..... provided you keep the water clean, the nitrates low, and the fish don't harm each other or be harmed, i can't see the problem.

lots of fish are used to packing themselves into very small spaces in nature, especially shoaling species like cories.

keep on top of those water changes!

MatsP · Post by **MatsP** » 04 Jul 2005, 09:59

jen.nelson wrote:Yup, as with so many things in life, there's not one right answer - there's lots of things that work for lots of people under lots of different circumstances. The nice thing here is that, for the most part, folks can discuss their different ideas without it becoming unfriendly.

Well, there's ONE answer to how many fish you can keep in a certain tank-setup. It's just not as simple as "It's a X g tank". You also have to factor in what water surface area, circulation, filtration (both which type and what media), exactly which fish, the water change factors (frequency/volume), and lots of other things.

--
Mats

Starsky · Post by **Starsky** » 05 Jul 2005, 16:12

jen.nelson wrote:Yup, as with so many things in life, there's not one right answer - there's lots of things that work for lots of people under lots of different circumstances. The nice thing here is that, for the most part, folks can discuss their different ideas without it becoming unfriendly.

I would add that, while this site is great for getting an idea of what works for other folks, there really is no substitute for observation - the fish will tell you what's going on by how they're acting, and it's important to be keyed into that...

Best,
Jen

Very well said.

Starsky · Post by **Starsky** » 05 Jul 2005, 16:19

racoll wrote:i would say 24 cories in a 15G sounds like too many.

BUT..... provided you keep the water clean, the nitrates low, and the fish don't harm each other or be harmed, i can't see the problem.

lots of fish are used to packing themselves into very small spaces in nature, especially shoaling species like cories.

keep on top of those water changes!

Yup, I have gone obsessive compulsive on the water changes. I make sure aeration is adequate, too. I think my cories agree. They all look very happy. I am even seeing some breeding activity going on. But I am not counting the chicks before the eggs hatch (pardon the pun). I plan to get a bigger tank eventually. We'll see how that goes.

Starsky · Post by **Starsky** » 09 Jul 2005, 03:34

I am getting six corydoras julii tomorrow. Quite excited because I have been looking for them for months now. I guess this clinches it. I've already prepared a 20 gallon tank for the new guys and will move in some of the other cories from the old tank there.