Possible Mistake with 110G Cichlid Tank

There are several problems with your stocking. The Oscar will eventually snack on the giant danios, firemouths are kinda wussys and only get 6" inches max usually and green terrors can get up to twelve inches. Along with that firemouths grow slow and green terrors grow at snail speed so as the oscar gets bigger they might be eaten or fall to aggression from the severum as it already shows itself to be aggressive. Another thing is that I think it would be best to not use the gallon per inch rule when stocking cichlids. You will need to cut down on your stock before anything mentioned above happens.

Lastly what kind of filter do you have running on the tank?

Also do you know the dimensions of the tank?

Tank is 4 or 5 ft long? (I've seen both for 110s) The inch per gallon 'rule', if that's what you're thinking of in adding up inches of fish, is more a guide for beginners with typical community fish and relatively meaningless with cichlids, where you have to consider territory, fish girth and not just length, feeding habits (oscars are notoriously messy fish needing a lot of water volume and strong filtration), species aggression and other factors. Some cichlids you can stock heavier than 1" per gallon and some, like oscars, need a lot more than a gallon per inch.

While the fish are small, maybe no problem in your tank, but as adults-- If it's a 4 ft tank the oscar plus some odd dithers or catfish may be about it. Or severum and green terror or firemouth might work if they tolerate each other (I've had sevs and green terrors get along well.) If it's a 5 ft. tank, you could do a little more with right mix. But you're also underestimating potential max size of some of those fish. Green terror males can get 9,10 inches easy, some larger. Severums also, except for rotkeils, 8 inches is on the small side. 9,10 inch sevs are common and they can get larger than that.

You're correct about aggression. Fish that are 3,4 inches are often not displaying their adult temperament, especially with a larger but tolerant fish in the tank. At this point they're respecting the larger fish, but when they start putting on size of their own and hormones get rolling things can change pretty quick.

Your sev was in the tank longer and claimed it. I had the same problem a while back. Why dont you think the sevs are real cichlids ? And if you always wanted a tiger oscar why didmt you start out with one

Anyway seems like your lfs was doing what most lfs do...making money off of you. As others have said that tank wont work out long term with that many fish. I would leave the sev, gt and firemouth with some dithers.


Or rehome everyone start from scratch and get the fish you want most then build around it.

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IMO, assuming the more common 110 gal length of 4 ft, you have three reasonable options.

1) Decide whether the oscar will be the anchor fish for the tank or not. If not and you want a display of several cichlids, the oscar probably doesn't fit the tank. If yes, the other cichlids-- or at least most of them-- should go eventually. 12 inches is not the max for an oscar. If you did a bell curve, the peak of the curve would be more like 12-14 inches, but they can get a few inches larger. An oscar and one other decent sized cichlid would be cozy in those dimensions, but might be possible if the oscar is amenable.

2) Play it by ear, let them grow a bit, see which of the fish are getting along, which you really want to keep, and adjust your stock accordingly. Any of those cichlids can vary in aggression by individual, so there's no single formula for how they'll do together, and since aggression is often relative to a particular tank and what's in that tank, adding or removing fish can also change the dynamics of how they get along.

3) Plan on a bigger (longer) tank if you want to keep them all together with the oscar.

IME with green terror size (for males), if you plotted them on a bell curve, 9 inches would probably be at the peak of the curve, 10 inches close to the peak, 11 inches not far off the peak, 12 inches possible but less common. In other words, more often than not a male will exceed 8 inches ime.

Not telling you absolutes, as in there's no way this or that will or won't work or as though there's an absolute cosmic and moral truth in gallons about how much space makes this or that species happy or unhappy. Sometimes you just have to see it in your own tank and see what works for you. On the other hand, you should know that some of your estimated max sizes are at the low end for some of those fish. With good care they're capable of being larger than those estimates and all together would make a crowded tank once they're grown.