acro tips bleaching

[AT]

2 weeks ago some of my acros started bleaching on the tips. I changed 10% water and tested params .2-3 days later I noticed one of my return pumps was blocked by a snail shell and was barely flowing.Could this have caused the bleaching.My alk was low around 7 yesterday. cal 430 phos 0 nit 0 They are not getting better. All the lps and clams are fine

 

[Dejavu]

From looking at your pic on anther site. I would have to say it's alk burn. I would slowly increase your alk. I prefer to keep mine around 9 dKh but 7 is ok, stability in more important.