[Delphinus]

I dunno, if that were my tank I'd have one already. They're pretty voracious eaters of most filamentous algaes. I've had some before, for me they seemed to last anywhere from six months to a couple years, they would go on and off the powerheads all the time, but a couple eventually did get stuck and that was the end of them. But, after a year or so of going on and off the intakes. So it led me to wonder what their natural lifespan is anyhow, and if old age was a factor to their demise that way. I dunno I could be way off. Since they seem to be prone to starvation (the other common cause of losing them), the thing to do is have them clean up your tank and then consider selling them for the next person having similar troubles. Or, try feeding them rolled nori sticks like you would for a tang, the ones I had that figured out that this was food were the ones that lasted the longest for me. Never had a tank wipeout from them, I'm not sure if this is a species specific thing or what, or if it's like cucumbers - when attacked by a predator maybe the risk is higher?