How many fish can/should be added at one time , into an established tank?

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Jayfish7

Jack Dempsey
MFK Member
Apr 12, 2014
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New York
How many fish can/should be added at one time , into an established tank? and how long before adding more?.. (to not screw with the bio too much!).. all advise is really appreciated! ;)
 
I'm adding 70 fish + 15 shrimps at once to a tank (190) that's just finished cycling.

I feed the tank with 20 ml of ammonia which the filter breaks down within 24h, which my fish (mostly Cory's,otos and tetras) won't be able to produce, so it should handle them.

What size tank, what filter and what type of fish and how many fish are ou adding?

If you have no fish, try feeding the tank with ammonia and take reading the next day of ammonia and no2.

No3 will of course be produced, but that's what water changes are for.

Try getting 4-5 ppm of ammonia in your tank, and see if it's removed within 24h.


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180g .. i had 3 fish for a while... added 3 more yesterday, but wanted to add a group of 5 schooling fish as well to break up the aggression... (so it would be 8 fish in 2 days.. all of which are under 4")...
 
180g .. i had 3 fish for a while... added 3 more yesterday, but wanted to add a group of 5 schooling fish as well to break up the aggression... (so it would be 8 fish in 2 days.. all of which are under 4")...

If you have test kit, use it and pay attention to readings, perhaps more frequent water changes for a few weeks and don't over feed.

It should probably go well, as long as these are fishes suitable for a 180 and you have good bio filtration.

But test kit is a must IMO, they will tell you when to change water and how your filter handles the bio waste.

Ammonia and no2 should read 0.

No3 is ok to have some, just don't let it go high, and stay on top of water changes.

Good routines with water changes is good for the fish, and as I've recently experienced high no3 will basically invite algae to manifest.






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I would think the answer is based on tank size and type of fish.

I'll guess about 25% of full stock max for a tank at a time. I think you could get away adding more tetras or guppys to a tank then something like plecos or cichlid.

I'll say about 2 weeks inbetween to make sure everything is ok.
 
I'm adding 70 fish + 15 shrimps at once to a tank (190) that's just finished cycling.

I feed the tank with 20 ml of ammonia which the filter breaks down within 24h, which my fish (mostly Cory's,otos and tetras) won't be able to produce, so it should handle them.

From a bio standpoint, this is spot on. The bacteria in the tank are a key limiting factor in how many fish can be added at any one time. Even one fish might be too much if the bacteria is too few and the one fish being added is too large.

After the bio is considered, there is simply the obvious concerns with pecking order, territories, individual fish size, fish behavior (shoaling or not), etc. There is no single rule on what is an acceptable amount to add or not add at one time. If I am adding shoaling fish and they are the right size and will adapt well in a large understocked tank, adding 6 at once might be best if the bio can handle it. Otoh, if the tank is fully stocked with aggressive cichlids, adding two new aggressive cichlid might be one too many (if not two too many.)
 
I was curious to know, if not feeding the bacteria with ammonia for 6-7 days, would it reduce the filters breakdown performance?

I'm very busy this week, and I'm getting all my fish on Thursday/Friday and I'm not sure if I can do water changes 2-3 days before I get them due to long work days, so I might just make it ready for them tomorrow and do readings before adding them.

Won't be feeding the fishes for the first day, then the next day I feed, then two days before regularly feeding stars.

I'm going home to parents for family wedding the same day fishes arrive, and I have to stay over the weekend. But I'll sneak a way once a day to check on them.

Couldn't be worse timing, I've been dreaming and planning to own a 190 gallon tank longer then the engaged couple know each other.... Better be Gordon Ramsey preparing the food at the wedding.


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You should have no problem after a week with finding most of the population still there. Many people with large fish will often go many days without feeding, in fact some fish go on hunger strikes and don't eat at all for longer than a week. The BB survive.
 
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