help fish start dying

[Megalodon]

Originally Posted by mohammadali

Hey folks
i bought this sea cucumber
is it normal with this cucumber ?
i had one before i sold it and i never seen this kinda before but i bought it from store like this

OMG!

That's your main problem. Flush that thing ASAP. Google "cuke nuke".

Do more massive water changes. Run lots of carbon.

Buy some test kits and learn how to use them. Either the LFS stressed that cuke or you did. If you did, you still have secondary issue(s) like the improper acclimatization of that cuke and/or poor water conditions.