Do you only have one cave in that tank? It sounds like if because everything first goes into the snakeheads cave, then runs behind a filter. Ummmmmmmmmm yeah, that's fair. SH with established territory and other fish with no where to go at all. How about, put in other hiding spots for the other fish, that way one isn't always stressed and swimming while the SH comfortably watches them. Im not saying SH's aren't mean, ive owned a few and can vouch, they are sick predators. But, I have had Jags live with Giant SH's for a while until they were outgrown. Dovii also have very large teeth when grown, up to 1/4 inch, which is about on par with that snake heads dentition. All im saying, is give the other fish a chance to get comfortable with their surrounds and allow them retreats if needed. Your snake head will need to be by itself when grown, or with verrrrrrrry large tank mates, larger then what a cichlid other then maybe a Tremisis will grow. Just saying, don't send fish to their death. Hell, I wouldn't put anything in with a Jag that was established with only one cave in the tank, it would kill the other fish just the same. That is essentially "Their tank"