[sddfd]

>abiotic algae

What specific species are you referring to?

>Blue-green algae produce oxygen.

That is only true during daylight. At night algae consume oxygen.

Independently, photosynthetic activity can increase pH values drastically.

[dredmorbius]

Specific mechanism is described here. It's the bacterial decomposition of the algae rather than the algael bloom itself which directly prompts the issue.

A bit of hair splitting, but useful for understanding what's going on.

https://articles.extension.org/pages/45651/if-algae-produce-...