Can I also suggest "more" frequent water changes
I try to change 10% weekly. If that's not possible, I will then do 20% on 2 weeks.
I've had 3 of my angels for almost a year now(christmas)
As far as acclimating them, I float the bag for 15 min and then gradually start adding "my" tank water to the bag.
45 min later, I empty all the water from the bag into the sink and just add the fish to the tank.(this is what has worked for me)
Good luck and keep us posted.
You can also buy the liquid master test kit for around $20 for FW
It includes PH
, Ammonia, Nitrite, Nitrate, KH