I have a 75 gallon freshwater tank set up since 2006. I got a terrible case of red and slimy green algae this summer when I didn't do my usual maintenance water changes for awhile and then went on vacation. I took out all the rocks and plastic plants, did multiple water changes (25%-50%) over about 2 weeks but then had floating algae (green water) for awhile. I added 3 live plants and the water is pretty clear, water tests all within normal ranges and good. I have 4 Buenos Aires tetras, 3 Columbian tetras, 2 blue gouramis, a pleco, 3 black skirted tetras, 3 serpae tetras. The biggest fish is a BA tetra who is about 3-4 inches long. The rest are fairly small. All doing fine and seem healthy, eating fine etc. I had them all before the algae problem--some over a year. I decided to add 5 Tiger Barbs. Within 24 to 72 hours, all died. More water changes, added the 30 day replacement fish and all died again. This has happened 4 times now. What am I doing wrong?