I had a bacteria bloom be so bad it made the water look like milk. This bloom happened after I cleaned my filters and did a huge wc all at the same time.
Clean out lots of this good bacteria at once and you throw off the balance. The good bacteria we need for a tank to be cycled will use up O2 to reproduce and multiply. A large bloom will depleat the water of o2 and cause stress to fish and will Cause fish to gasp at surface. This is what my fish were doing. I did lose a red severum to this bloom before I knew what was going on.
I added a power head to the tank for added surface agitation this helped get the o2 back in the water. Doing this helped my fish go back to normal. Then I just waited for the bacteria settle by not touching the tank. once it grows back the right amount of lost bacteria everything is normal.
So my guess is bacteria bloom due to cleaning to much at once. The photos look just like how my tank looked.
80gal planted Angelfish community.
100gal SA cichlid, Silver dollar, and delhezi. No plants!
36 gal Planted Swordtail community.