Neither
Carinotetraodon irrubesco nor
Carinotetraodon lorteti are brackish water, though I'm sure they will tolerate slightly brackish water perfectly well. They are not fussy about water chemistry at all, but neutral, slightly soft to moderately hard water is perhaps the ideal.
In my experience,
Carinotetraodon irrubesco do well singly and in pairs. If you have sufficient space, you can keep multiple pairs. I had no problems at all keeping a pair in 180 litres. Conversely, in very small tanks, less than 80 litres, my experience is that
Carinotetraodon irrubesco tend to be rather shy.
Carinotetraodon lorteti are substantially more aggressive, though this does vary from mild nippiness through to outright hostility. You'll notice that groups of
Carinotetraodon lorteti exhibit circular bite marks on their flanks far more often than
Carinotetraodon irrubesco.
Carinotetraodon lorteti are best kept singly or in groups of one male with one or more females, as space permits.
Cheers, Neale
My lfs has gotten in some Red Eye Puffers. They are selling them as brackish. All my research leads me to beleive they are actually fresh water fish. Can anyone confirm either way?
Also, what is the minimum group size they should be kept in?