Based on the condition of your green BTA it looks to me like your GBTA is negatively influencing your new RBTA. BTAs don't always move to what we think are more advantages positions. I have had several move behind rocks and then die from lack of light.
Based on the condition of your GBTA, the conditions in your tank are good enough for a BTA to thrive, yet the newcomer is not. There is nothing obviously wrong with the RBTA, in fact it actually looks OK except that it is not expanding like it should or was originally. That leads me to believe that you have some intra-species competition going on and the RBTA is losing.
My suggestion would be to find a new home for one of your BTAs.