yea i've bought ~20 small NTT's almost a year ago and have grown them out to 5-8". out of the 20, about 3 of them died for what I thought to be no real reason.
i did notice after the first one died that when they breathe hard and dont really swim around, they end up dead the next day. i tried treating them in a hospital tank with meds, salt, etc but im 0-2 in trying to save them. the 3 fish died on seperate occassions, with a few months time between deaths.
i've bought 5 small IT's 1-2" and none have died on me yet.
i think its safer if you buy bigger size NTT's, maybe 6"+ is better