Two juvenile betta fish, dead. Each in a Imagitarium 6.8 gal. planted tank. Established tanks, water checks out very good. The only other living things in tanks are a few snails, a bristlenose pleco in one tank & a clown pleco in the other. Both tanks have cherry shrimp that were there when young bettas, one about 1 1/2" the other, a Galaxy Koi about 1 inch, were introduced. One betta arrived Jan. 14th, one on the 19th. Different sources. The first one died 9 days after arrival. From day of arrival he hung out exclusively in the back corner of the tank, ate the first day but went right back to corner & hung there. The Galaxy Koi, who arrived on the 14th, has been a super friendly little kid, all over the tank, investigating as is normal. Last night he was his usual, happy self. This AM I found him dead, with about half dozen cherry shrimp on him. I'm SO sad about this & don't know what to do. We're not exactly novice fishkeepers. Have cherry shrimp & plecos in almost all of our tanks, other than the larger cichlid tanks. We would appreciate any help here as we want our pet bettas. We don't want them terrorized & then killed by 'somebody'. We do know that shrimp & plecos will eat a fish, but we thought, AFTER the fish is dead, then they clean up. Something or somebody killed our little guys. But, who?