How Many Fish Can I Add At Once?

[Aquamagic]

I have a cycled 10 gallon tank and yesterday, I purchased 4 Cardinal Tetras. I put 4 of them in the 10 gallon and took out the Amano Shrimp in there and placed it back into my 5 gallon. Now I have one more Cardinal and I was wondering if I could put it in the 10 gallon tank without putting too much fish in at once.

 

[Randi]

In a 10 gallon I wouldn't recommend adding more than 2 fish at a time. However, if you did a fishless cycle starting with 4ppm ammonia you should technically be able to fully stock your tank right away. Check your levels and if the 4 fish didn't cause an effect one more shouldn't either.

 

[Aquamagic]

Does this rule apply even if I have a filter made for a 20 gallon tank?

 

[Randomitity]

You can have a 40 gallon tank filter for a 10 if it doesn't have all the bacteria it wouldn't do much still

 

[Aquamagic]

But this filter does have all the bacteria because I used to use it for a 5 gallon with a Betta and 3 amanos before I moved it to my 10 gallon.

 

[N0body Of The Goat]

But this filter does have all the bacteria because I used to use it for a 5 gallon with a Betta and 3 amanos before I moved it to my 10 gallon.

So unless this filter has very recently been used in a bigger stocking than the Betta and 3 Amano Shrimp, the filter will at best have a bacterial colony capable of cycling the waste products of these four creatures. Having now put that filter in with four Cardinals, which in all likelihood is an increase in bioload over one fish and several shrimps, the bacterial colony in that filter needs to play "catch up" i.e. increase in size.

Consequently, it would be far safer to not add anything else to the 10 gallon for about two weeks, while in the meantime monitoring the water for ammonia and nitrite spikes (being ready to do >50% water changes if such readings show up).