Schooling fish and killifish questions

Sgooosh

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1. Can I keep different types of schooling fish with my harlequin rasboras? I have 12 rasboras right now, can i keep for example 5 cardinals with them? or do I have to have 10+ of each?
2. Can small killifish go in a 75g peaceful community? or do they have to be in a smaller tank?
 
#1 You need 10+ of every species of shoaling fish in a tank. So 10+ harlequins and 10+ cardinals.

#2 I'll leave for the killifish experts
 
#1 You need 10+ of every species of shoaling fish in a tank. So 10+ harlequins and 10+ cardinals.

#2 I'll leave for the killifish experts
thanks. Can I add them gradually? I don't want to add too many fish to the tank at once
 
Most killies would vanish in a 75. They're small, peaceful, easily bulled and shy. Also there also aren't a lot of species that would live well in the temps cardinals or harlequins would. Under the African rainforest canopy, the sun doesn't warm the water and temps around 20-22c are common. Cardinals are up at 26, and that would shorten killie lives quickly.

How you add tetras depends on whether you quarantine. You can add 5 at a time to space it out, but you don't need to. Plus, every new purchase not QTed is a risk to everything in the tank. If I didn't QT, I would take my chances on adding as large groups as I could find. The addition of 10 small fish won't upset the cycle in a tank that size.
 
Shoaling fish should be added the whole shoal at the same time. But I appreciate that adding a whole shoal would just about double the bioload.

Remind us, does the tank have live plants, and if it does how many and fast or slow growing?
 
Shoaling fish should be added the whole shoal at the same time. But I appreciate that adding a whole shoal would just about double the bioload.

Remind us, does the tank have live plants, and if it does how many and fast or slow growing?
more than half the tank is densely filled with fast growing temperate aquarium plants
Most killies would vanish in a 75. They're small, peaceful, easily bulled and shy. Also there also aren't a lot of species that would live well in the temps cardinals or harlequins would. Under the African rainforest canopy, the sun doesn't warm the water and temps around 20-22c are common. Cardinals are up at 26, and that would shorten killie lives quickly.

How you add tetras depends on whether you quarantine. You can add 5 at a time to space it out, but you don't need to. Plus, every new purchase not QTed is a risk to everything in the tank. If I didn't QT, I would take my chances on adding as large groups as I could find. The addition of 10 small fish won't upset the cycle in a tank that size.
thanks. I think in a 15 gallon they can breed more.
 
I concur with above members that the entire intended group of a shoaling/schooling species should always be added together, in both a display tank or a quarantine tank. The fish will definitely settle in much faster the more there are, which means even less chance of ich or something else. With feisty species that may have an hierarchy this is extremely important for this reason as well.

With plants as described, you really cannot possibly overload the system. The amount of ammonia/ammonium that fast-growing plants assimilate is considerable.

The killifish issue I leave to those like Gary with more direct experience. But I will say that there are many small sized species that really do not do well in large tanks for a few reasons.
 

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