I bought four of these about a month ago, and they did fine for about 2 weeks. Then I lost one. Yesterday I found another dead one.

My pH is between 6-6.5, Ammonia 0, Nitrite 0, Nitrate 20. The tank has been established for about 3 years. I have lots of Java moss. Most of the other plants are eaten. I have never seen the red lizards eat (besides what they are scraping off the glass and wood), but I assumed they must be eating.
I think I may move them to either my Bristlenose nursery or my quarantine tank where I have several very young, small peaceful fish in quarantine. Both tanks are heavily planted. The Bristlenose tank has a good colony of gammaras shrimp.
Could you give me any advice on what I can do for these incredibly beautiful and interesting fish? I would like to get a few more, but only if I can provide a decent habitat for them. I would like to enter them in our state fair in February, but only if I have them in good condition. Thank you.