actually, that's a very bad generalization. a lot of triggers stay within the foot long range. picasso (humu humu), rectangle, undulated, crosshatch, niger, blue jaw and the bursa triggers all stay within 10-13", to name a few. in fact, less triggers grow to the 2ft mark. queen, titan and clowns are the most easily found triggers that grow to large sizes (over 13").
and most triggers, as i've already stated, are aggressive towards conspecifics. it may work for a little while, but one day a trigger might snap and destroy its tankmate(s).
if you absolutely want to add multiple triggers, add some of the less aggressive ones like the niger, blue jaw, and bursa in a large tank.
This maybe a lucky situation but I currently have a Niger, Humma, Bursa, and an Ungulated tigger all in the same tank... I've had them all in the same tank sence they were about 2inches and they all do fine they have there days when they fight pretty good especailly when I rearrange the tank but all is well for the most part... But like I said it all matters with the tank size, because what I noticed is that they are more territorial then killers with the exception of my ungulated trigger he is just down right nasty but my Grouper Keeps in check... For how long I dont know but we will see!!!
Ya I had a picasso/huma huma trigger in my 75g fowlr tank for like a month. He was fine at first but then he went on a snail killing spree and then finally he bit me when I was cleaning the tank. That was the end of him, he went to the lfs and was traded for a mated pair of maroons that are a lot easier on both my snails and hands. I still love triggers dont get me wrong. I plan on turning my 75g into a trigger tank once I get my 150 set up. Later
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might be better off with the 150 as the trigger tank. I had a huma huma that bit me a couple of times too. he also tore a porcupine puffer that was bigger than him to shreds one day after getting along fine for months
I keep a pinktail, CT, Black Hawaiian, and blue jaw together. All are about 5-7"
They have been together for 2 years now. I believe that by providing ample hiding spots and feeding often helps to diminish their aggression.