Overstocking? Tank size vs. filtration capacity

[SilverSageClev]

How important is tank size vs filtration capacity when it comes to stocking?

I’ve had tanks for years but I’ve always sort of guessed at stocking based on the old “one gallon per inch” rule. I know it’s not a very good rule but honestly I don’t have the experience to do anything more specific.

I want to add a few fish to my 29 gallon tank because my husband added a mollie and a swordtail to my tank on a whim and without my permission. I’d love to add two more mollies and two more swordtails. As adults (they are currently pretty small) this would put me at 1” under the maximum inches according to this rule. The other inhabitants are kuhli loaches, guppies, a snail, ghost shrimp, and a Bristlenose pleco (also currently tiny).

Usually I don’t like to push the limit on numbers because I know the rule I’m using is not all that reliable, but tank is planted and has TWO 30 gallon WhisperIQ filters.

Considering the plants, filtration, and current inhabitants, what are your thoughts on the proposed additions?

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[Jeremy180]

Inches per gallon is pretty much a useless comparison.
The three main factors in determining when a tank is overloaded are:
1:Room for adequate exercise.
Generally a tank should be at least 5 (for inactive fish like bushy nose pleco) to 8 (for very active fish like glow light danios) times the (fully grown adult) length of the fish, plus an adequate front to back width that the fish can easily turn around.
2: Bioload: this is directly related to a fish's waste output which goes up exponentially faster than the length.
3: room for territories.
many fish in nature will stake out an area in nature and chase any fish that comes too close to an acceptable distance from this location.
The problem is, that for some fish, an "acceptable distance" could be farther than the length of the tank, resulting in constant harassment and chasing in tanks that are too small

 

[Colin_T]

Hi and welcome to the forum

Give hubby a slap across the head for doing this

Any idea what the general hardness (GH), carbonate hardness (KH) and pH of your water is?
Livebearers (mollies, swordtails, platies, guppies) all need hard water with a pH above 7.0. If the GH is too low they will have problems.

As a general rule you want the GH to be above 200ppm for guppies, swordtails & platies. And you want the GH above 250ppm for mollies. The pH for all these fish needs to be 7.0 or above, preferably around 7.4-7.6. Higher than this is fine but they won't tolerate a pH below 7.0.

--------------------------
If you can provide us with the tank dimensions (length x width x height) it will give us more to work with. Length and width are more important to fish because they swim horizontally not vertically.

Surface area (length x width) is a major consideration in working out how many fish can go in the tank. A tank that is 2 foot long x 12 inches wide x 2 foot high might hold a lot of water but doesn't have much swimming space for the fish. If the tank was 4ft long x 12 inches wide x 12 inches high it could hold twice as many fish as the aforementioned tank, purely due to the surface area.

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I don't like mixing swordtails with guppies because the swordtails can bully the guppies and cause problems. If you can return the swordtail it would be better for the guppies. Alternatively move it into another tank.

Any idea if the molly is male or female?

Are the guppies male or female or both?

If you have female livebearers they will probably be pregnant and give birth to live young for the next 6 months, regardless of if there is a male. This is due to the females carrying sperm packets from previous matings. The females can carry up to 6 sperm packets and they use 1 packet per batch of eggs. The female carries the eggs and babies for about 1 month before giving birth to free swimming young. They can then use another sperm packet to fertilise a new batch of eggs.

If you have a number of female fish in this tank, you could quickly have lots of baby fish that will populate the tank and you will need to remove some of them to prevent overloading the tank.

I prefer to keep livebearers in separate sex tanks, all male or all female. This reduces stress from the males constantly harassing the females and reduces the number of unwanted fry. If you want to breed them, try to keep at least 6 females per male, or borrow a male every 6 months and let him mate with the females, then get rid of him.

 

[CometBetta]

They may be small now but in the future an adult swordtail requires about 15 gallons! Since yours is a 29 gallon getting 2 more swordtails is definitely overstocking, they would get very big and you wouldn’t want to get yourself in a big overstocking situation once they all grow up. Guppies usually get around to 2 inches long. So using the one gallon per one inch you would keep around 5 guppies in a 10 gallon. Also.... a PLECO?? At pet stores they are usually so tiny and people get them and put them in small tanks since they are so tiny. But once they grow up you need 29 gallons for them! And loaches get big as well. One grown up one would need about 10 gallons. So basically, 29 gallons minimum for the bristlenose pleco, 10 gallons minimum for the kulhi loach, 10 gallon minimum for 5 guppies, 1 gallon minimum for snail, 1 gallon minimum for 8-10 ghost shrimp, 15 gallon minimum for a single swordtail, and 29 gallon minimum for Molly’s because they can grow to 6 inches long. So once they are all adults it will definitely be overstocked so you should prepare big tanks for most of them.

 

[Jeremy180]

Sorry, went off on a bit of a tangent.
Anyway a standard 29 gallon is 18" tall by 30" long, and 12" front to back. (I should know, measured mine dozens of times, lol.)
I am not an expert in stocking, but I feel adding more fish might be pushing it once they all reach full size, especially if the Molly is a sailfin.

 

[The Lumpfish Guy]

I like to use Aquadvisor as little tool to help inform my decisions. It's not perfect and I use my judgement on the results, but It can be helpful in preventing from going really wrong.
Page seems to be down at the moment though
http://www.aqadvisor.com/

 

[Jeremy180]

While Aqadvisor does give a somewhat more accurate ballpark than inches per gallon, (not really a high bar to set, frankly) I have noticed that it tends to miss a lot of incompatibility issues, and often underestimates both the bioload of larger fish, and the minimum tank size for semi aggressive fish and very active fish.
At the same time, some very low bioload creatures, like boraras and especially shrimp tend to have somewhat overestimated bioload.

And most glaringly there is no comment whatsoever on the difficulty of keeping temperature, ph, and ammonia/nitrite stable in tanks under 7-10 gallons.

 

[The Lumpfish Guy]

While Aqadvisor does give a somewhat more accurate ballpark than inches per gallon, (not really a high bar to set, frankly) I have noticed that it tends to miss a lot of incompatibility issues, and often underestimates both the bioload of larger fish, and the minimum tank size for semi aggressive fish and very active fish.
At the same time, some very low bioload creatures, like boraras and especially shrimp tend to have somewhat overestimated bioload.

And most glaringly there is no comment whatsoever on the difficulty of keeping temperature, ph, and ammonia/nitrite stable in tanks under 7-10 gallons.

I agree it has it's limitations, as would any model. But It still can be a useful tool IMO

 

[SilverSageClev]

Hi and welcome to the forum

Give hubby a slap across the head for doing this

Any idea what the general hardness (GH), carbonate hardness (KH) and pH of your water is?
Livebearers (mollies, swordtails, platies, guppies) all need hard water with a pH above 7.0. If the GH is too low they will have problems.

As a general rule you want the GH to be above 200ppm for guppies, swordtails & platies. And you want the GH above 250ppm for mollies. The pH for all these fish needs to be 7.0 or above, preferably around 7.4-7.6. Higher than this is fine but they won't tolerate a pH below 7.0.

--------------------------
If you can provide us with the tank dimensions (length x width x height) it will give us more to work with. Length and width are more important to fish because they swim horizontally not vertically.

Surface area (length x width) is a major consideration in working out how many fish can go in the tank. A tank that is 2 foot long x 12 inches wide x 2 foot high might hold a lot of water but doesn't have much swimming space for the fish. If the tank was 4ft long x 12 inches wide x 12 inches high it could hold twice as many fish as the aforementioned tank, purely due to the surface area.

--------------------------
I don't like mixing swordtails with guppies because the swordtails can bully the guppies and cause problems. If you can return the swordtail it would be better for the guppies. Alternatively move it into another tank.

Any idea if the molly is male or female?

Are the guppies male or female or both?

If you have female livebearers they will probably be pregnant and give birth to live young for the next 6 months, regardless of if there is a male. This is due to the females carrying sperm packets from previous matings. The females can carry up to 6 sperm packets and they use 1 packet per batch of eggs. The female carries the eggs and babies for about 1 month before giving birth to free swimming young. They can then use another sperm packet to fertilise a new batch of eggs.

If you have a number of female fish in this tank, you could quickly have lots of baby fish that will populate the tank and you will need to remove some of them to prevent overloading the tank.

I prefer to keep livebearers in separate sex tanks, all male or all female. This reduces stress from the males constantly harassing the females and reduces the number of unwanted fry. If you want to breed them, try to keep at least 6 females per male, or borrow a male every 6 months and let him mate with the females, then get rid of him.

Hi, I’m working on the hardness and Ph etc at the moment with our local petsmart, since when I took my water in to petco they just said “it’s fine” with no additional details. I just did a water change and I was told to wait 48 hours before testing again.

All the guppies are male, the molly is male, the swordtail is female. I do NOT want to breed. My male guppies have shown no problems with bullying each other and the additions don’t seem to have messed with that so far.


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[NickAu]

Im sorry but Rihnos are not aquatic animals so should be removed before they drown LOL, having said that I am serious about removing the plastic rhinos unless you are certain the plastic is food grade and aquarium safe, they could leech god knows what chemicals into the water.

 

[SilverSageClev]

They may be small now but in the future an adult swordtail requires about 15 gallons! Since yours is a 29 gallon getting 2 more swordtails is definitely overstocking, they would get very big and you wouldn’t want to get yourself in a big overstocking situation once they all grow up. Guppies usually get around to 2 inches long. So using the one gallon per one inch you would keep around 5 guppies in a 10 gallon. Also.... a PLECO?? At pet stores they are usually so tiny and people get them and put them in small tanks since they are so tiny. But once they grow up you need 29 gallons for them! And loaches get big as well. One grown up one would need about 10 gallons. So basically, 29 gallons minimum for the bristlenose pleco, 10 gallons minimum for the kulhi loach, 10 gallon minimum for 5 guppies, 1 gallon minimum for snail, 1 gallon minimum for 8-10 ghost shrimp, 15 gallon minimum for a single swordtail, and 29 gallon minimum for Molly’s because they can grow to 6 inches long. So once they are all adults it will definitely be overstocked so you should prepare big tanks for most of them.

It’s a Bristlenose pleco which I was told will only get 4-5” max. The loaches are Kuhli loaches which I was told max out at about 3-4” but that a group of 4 can do great in a 10 gallon with low bioload tank mates. The guppies are all males which don’t get as big as the females. As for mollies, the info I’m finding says the common mollies get up to 4” max for females, 3” max for males? I’ve never seen or heard of a 6” molly...


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[SilverSageClev]

I like to use Aquadvisor as little tool to help inform my decisions. It's not perfect and I use my judgement on the results, but It can be helpful in preventing from going really wrong.
Page seems to be down at the moment though
http://www.aqadvisor.com/

I tried that first no idea why it’s down or for how long. When I ran this tank through that system it said I had lots of extra filtration but that was before I wondered about adding.


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[NickAu]

Female Mollies grow to about 5 or 6 inches long and live for about 5 years.

 

[SilverSageClev]

Im sorry but Rihnos are not aquatic animals so should be removed before they drown LOL, having said that I am serious about removing the plastic rhinos unless you are certain the plastic is food grade and aquarium safe, they could leech god knows what chemicals into the water.

Thanks! My Rhinos are training for the olympics!

Jk, they are stone rhinos and have been in fish tanks for the last 5 years with no ill effects. To be more specific, no dead fish. However I’m now learning a lot lore about the chemistry of my water and if they seem to be causing trouble I will remove them.


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[NickAu]

Stone? then thats ok, I used to work in the plastics industry mixing and compounding the raw materials before they became plastic.