I'l get a bigger tank sooner or later.
Planning what aggressive and violent fisi I can get tho
A 10gal can be used as a growout for sometime. For example i have a 1" rhom when its full grown itll tip 15-16" so using that scale 10 gal at 1" = 150gal at 15" so obviously for a small baby fish its fine untill around 21/2"-3".
In regards i think you can apply the same theory to what you want! Be it a solitary rhom or a few 1/2 red belly piranhas, just prepare their big tank while they grow, although rbp grow like weeds so 3-4 babies in a 10 will only last 4 weeks max!
#1 S. Vettel