In my experience, (9 chromis) i would agree with the statement that some loss in the initial purchase is normal. I have lost 3 of the original 9 purchased. I did purchase them in two batches though. 5 the first time and then an additional 4. The three I lost were in the first batch. I lost none the second time. The only thing different that I can identify is I fed the second batch 3 - 4 times a day with much more food than I would consider they needed. No food ever hit the bottom though. After one week of heavy feeding, I backed off. The heavy feeding allowed even the weaker Chromis to get food and regain strength and recover from the move. Both batches of fish school together with no problem. I have a 150gal tank and currently have 6 2-3 inch chromis.