Hi. I don't know if this is the correct forum for this. I have a 230 gallon fowlr that has been up since January. I have 2 clowns that are fine, a pb tang that died very suddenly 2 days ago - I walked by and it was swimming normally and walked by again a minute later and it was dead, and a queen angel that has been actively dying over the past 2 days but still alive. I checked my params. Everything was normal except for some reason my ph was unmeasurable on the low side. Must be 6 something. I did a 30% water change with no affect on the angel or ph. I have ph buffer being delivered today. I tried raising it with baking soda to no avail. The only thing that's changed in the past week or so is that I no longer have algae growing on glass - there is literally nothing to clean(is that normal?), I've added pods to my fuge, and microbacter7. CUC is fine. I've had a slight diatom issue and what I think was/is black cyano I used chemiclean on a 3 weeks ago. It did not totally get rid of it, and I suctioned the rest out. Do you think this is a PH issue only or could something else be going on? Why would my clowns be unaffected? Any help would be greatly appreciated! Attached are pics of tge black stuff before I suctioned it, the angel and clowns.