Recently stripped down a very well established Jewel 60 and took out the internal filter. I installed the filter (very well matured with original uncleaned filter) into a temporary 10 gallon tank. Transferred inhabitants into the 10 gallon - 10 Cardinal Tetra, 3 Glowlight Tetra, 3 Amano Shrimp and about 30 Crystal Red Shrimp, along with some Moss and a couple of other plants. All been fine for 4-5 days. Just been away for the weekend (Saturday till Monday) and returned to find all the Cardinals dead. Shrimps are all fine and so are the Glowlights. Have not tested water yet but I would have thought if anything were wrong the Shrimp would be first to suffer. Any ideas please?