filter?

[Dissy]

Lord no... one placo at a time and both the cichlids were only an once a price the koi was just chillin till I get my 75 gal over here.... I didn't buy them all at once

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Your koi and texas cichlids aren't even temporarily compatible with each other. Koi is cold water fish, and cichlids are tropical fish. Neither can just "adapt".

Same thing with your plecos - not even remotely compatible with koi for the same reason.

Unfortunately, it's not surprising it died. I'm sorry.