Fish suicided in an interesting way

[Dearth]

One of my green chromis found a new game today it's called:

"Run head first into the power head impellor" game

All my chromis' love to swim up to the front of the power head and then let the flow push them away they have been doing that since the first week in my tank way back in sept. Well I was watching 2 of them do it today and out of the blue the third one just appeared out of nowhere and ran itself head first into the power head chamber where it had a short and very brief communion with the fish gods and it was the. Spit out sans part of its head. I have 2 chromis left as now the other 2 have since committed suicide and would like these 2 to stick around for awhile.

Do you guys have a trick to stop fish from swimming into the power head and communing with a higher fish power?