With the addition of the new LR
, I would also suggest checking the ammonia, you never know. Reaction to light can sometimes be from eye problems so be sure the eyes are very clear. If they do not show any sign of a problem, then I am unsure of why the reaction to light.
The red splotch at the base of the tail is a bacterial infection. If you have not just recently done a water change, I would suggest one soon. The bacterial problem can often be cleared up by simple repeated small water changes to reduce DOC
's and other nutrient sources that feed the bacteria. The addition of a good vitamin to the foods will also help the fish natural immune system to fight the infection. In stubborn cases, you may need to quarantine
and treat with a gram negative anti-biotic but I would start with the above first.
Are there any other tangs in the tank?