He has already been in saltewater a lot and about nano tanks in
DIY i think.
I see a trend here with some of your your posts..you keep asking for "small aggressive fish" and mentioned it should eat other fish in one wish list. Basically a fresh water piscevore that will some how fit in small space and still be out in the open.
Pirahna need to be in groups like many tetra, dicus, and other S.A specie
If you want to have something you can watch swallow other fish you need space.
Piscevore fish are usually either
A) much larger than their intended prey to avoid stressful struggles.. or
B) run in "packs" to attack large prey and overcome it.
many smaller carnivorous fish are ambush predators that hunt at night or from hiding places.
Salt water has a much larger selection of toothy maws that can still be housed in less space. Freshwater fish are opportunistic omnivores for the most part which is why they were considered "easier" than salt in the old timey days.
Currently you have one twenty? that is salt water? Since you said you had a
fowlr? and one that is
FW? two tanks then? Are you converting?...I am confused because your postings in
SW frorum.
And you are planning to get a 55 soon when your parent okays its location?
I have a polypterus that I plan as my culling machine. judging by what he can eat now..he will be good for the job. But he gets a 177 gallon tank this summer (larger if I make it a biotope. He just goes >gulp<. Pirahna are not all they are painted..you should see an awful thread in the Lounge where some guy throws a mouse in with them..the fish are obviously unerved by the "new" food . They kill it eventually but never eat it. My grandpas pirahna were boring , and messy. I always spent as long cleaning their tank as the goldies. and they used to bump my arm and beg for a feeding. The rest of the time they floated in a corner only turning the shoal direction to show they were aware of you or alive.I had some of his oddity fish bite me harder. The ate very small fish. Of course there are many pirahna. Leaf fish for an experienced fish keeper, or pike gourami. No others can take small spaces well. And don't confuse aggressive fish for fish eating fish. Even a goldfish will eat a smaller tank mate if it will fit down the hatch.
you neeed to list what you want the fish to do for you os we can help you find fits.