how many fish to add per week rule.. - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 9 Old 10-25-2011, 08:38 PM Thread Starter
how many fish to add per week rule..

I wanted to add some bloodfin tetras to my tank, but the "rule of thumb " is to add no more than 3-4 fish per week, since this is a schooling fish how should i handle this? 3 one week, then 3 the next or all 6?
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post #2 of 9 Old 10-25-2011, 11:18 PM
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Its not so much a per fish rule as it should be a percentage rule, if you had a tank of 50 fish then it would would be pretty safe to add 10 fish at once. Where if you have a stocking of 3 then adding 3 more will most likely result in a mini cycle not so much an issue as long as you keep an eye on your water parameters and do appropriate water changes. Of course there are a lot of variables such as how messy the fish are you are adding etc, just off hand it should be safe to add around 20% or less of your stock level and avoid a mini cycle for the most part. But since mini cycles usually only last a week or two and usually aren't all that bad most people will add in about 40% of their stock.

Of course there are always reason you might need to add more, such as introducing territorial fish at the same time so one doesn't claim the whole tank. Just use your best judgment on how much your bio filter can handle at one time.
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post #3 of 9 Old 10-26-2011, 04:23 AM
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I look at volume of water when adding fish.
In 50 gal tank ,one could add five or six small tetra's at one lick without possibly seeing ammonia or nitrite's creep up assuming the tank has healthy biological filter (cycled).
Adding six small tetra's to Ten gal tank, would be more of a worry for there is less volume of water to help dilute possible ammonia /nitrites.
In both cases..alway's good to monitor (test) after ten or twelve hours of placing fish and perhap's daily for a week or more to see that biological filter is keeping up with the waste produced.

The most important medication in your fish medicine cabinet is.. Clean water.
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post #4 of 9 Old 10-26-2011, 06:32 AM
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Also, is this tank planted? cycled?

I safely added 8 tetra to my 29g all at once without issue. My tank is very heavily planted though. Having plants really makes it easy.
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post #5 of 9 Old 10-26-2011, 08:13 AM
When you consider all of the variables, there really can't be a rule of thumb regarding adding new stock...

> New tank, recently cycled or established.
> Water chemistry.
> Size of the tank.
> Condition and maintenance of tank and substrate.
> Plants.
> (Bio) Filtration.
> Existing bio-load - proposed new bio-load.
> Feeding amounts and methods.

Any one of the above (and others I haven't thought of here) leaning on a negative side totally changes the equation. We must use our best judgement and better to err on the conservative side than to throw money away and torture poor defenseless fish.

If we have an established eco-system and make changes in stock, filtration and/or maintenance, we need to perform water tests and/or observe stock to better ensure against negative reactions. If/when there are negative reactions to change(s), we need to be prepared to perform corrective action(s) quickly as needed.

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post #6 of 9 Old 10-26-2011, 09:09 AM Thread Starter
55 gallon tank that has been cycled for 3 weeks, current fish, 5 zebra danios, 2 platys, did have 2 giant danios that were removed from tank. 8.3-8.4 really limits my selection of fish. No live plants . Running 2 fluval C4 on low flow
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post #7 of 9 Old 10-26-2011, 09:36 AM
Its been cycling for 3 weeks or it finished the cycle 3 weeks ago? If the cycle has completed I would think adding all 6 Tetras together would be okay in a tank that size.

30 gallon:
6 Harlequin Rasbora
2 Bolivian Rams (1M/1F)
4 Corydoras Melanistius
2 Peppered Cory
1 Sunburst Platy (M)
1 Guppy (M)
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post #8 of 9 Old 10-26-2011, 10:33 AM Thread Starter
Finished the cycle
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post #9 of 9 Old 10-26-2011, 12:22 PM
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I agree with all that others have posted. The entire system has to be considered.

In your case, add the 6 fish. Live plants would make this a non-issue. But even without, the time taken for bacteria to respond (= multiply) to an increase of ammonia and then nitrite in that large a water volume would be around 20 hours total, given your water parameters.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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