boxfishys need help!

[Scorpion]

ok... here it goes:

this past friday, we purchased 2 boxfishes (spotted boxfish and helmet boxfish, both no larger than an inch). this morning, the spotted boxfish was stuck on the intake of our powerhead motionless. i was scared that if it was very stressed or dead, that the toxins would kill other tankmates. so, i pulled him off and made the decision "terminate". i didn't know what else to do. we don't have an extra tank, or anything to quarintine it. and i couldn't take it back to the LSF because i had to go to work on the bus, and no one else here (my home) has time to go out (sister is at school, sister's BF is at work). i'm very sad that we lost one of our boxfish.

so... now... here's my main question. we still have the helmet boxfish, BUT it's not eating what we are feeding our tank. we feed them Omega3 rich brine shrimp (my sister wanted to get Omega3, being the health freak she is). we've also tried flake once, but without prevail. i'm worried that the same fate, that happened to the spotted boxfish, will happen to the helmet. i would be more sad if we lose all our tankmates just because our other boxfish dies. what should i do? should i take it back to our LSF? or should i try different foods or methods of feeding?

i think we made a mistake in purchasing these boxfish. i want to apologize to anyone that is sensitive to this situation (life, even animal's, was ended). if possible, i want to make ammends with God, and save the life of our boxfish (nicknamed "Sharky").

please help. thank you in advance.

** SIDE NOTE **
the LSF said that boxfish are fairly easy and fun to care for. but, when i did some research on boxfish in general, most sources say that boxfish should be left to experts. i did this research after the fact that we bought the 2 boxfish (we bought them cause my sister's BF got a kick out of watching them swim weirdly and look really funny).