Ime sevs become more aggressive if they're squeezed into too small a tank. Don't know the dimensions of that tank, but if it's 3 ft. or less, as adults you'd have to have a very cozy pair to not have trouble between them, and then you wouldn't want much else in the tank, few smaller dithers, small to medium pleco, a smaller cichlid-- maybe-- and even those could be trouble if the sevs are breeding. 4 ft. 50 gal tank, little better odds, but you'd still be pushing it a bit and would be depending on the pair having to go along with it-- again, not a given.
The ratio of sevs per gallon you can do gets better in a larger tank, larger dimensions. In other words, you might be able to do a group of 5 or 6 or so (depending on particular species) in a 125-- 15-20 gals per fish is still ok in such a tank, but ime it's not scalable down to smaller tanks, more so at less than 4 ft ime.
Single sevs with some other compatible (non-severum) fish in the tank usually do just fine.
The ratio of sevs per gallon you can do gets better in a larger tank, larger dimensions. In other words, you might be able to do a group of 5 or 6 or so (depending on particular species) in a 125-- 15-20 gals per fish is still ok in such a tank, but ime it's not scalable down to smaller tanks, more so at less than 4 ft ime.
Single sevs with some other compatible (non-severum) fish in the tank usually do just fine.
