I think I get what you mean: buy 60 "schooling fish" for $120-$600and quarantine them in the 90 vs buy 6 schooling fish for $40-$120 and put a light diffuser/mop/whatever equipment is needed to breed them, then breed 100 and give me some
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It depends on the fish and how significant the water parameters are for breeding. It's a pretty serious goal to churn out tetra, a little easier with some Rasbora. Are you thinking characin or cyprynids?
I'm looking at buying 40-60 rummynose or similar tetra pretty soon I bet there's a store nearby that might be able to help with wholesale pricing since the best deal on the Internet for these species is in a black out zone thanks to the local business policies they have agreed to... then there's always aquabid...