To dilute poisons/ toxic substances in the water, do one big (75-90%) water change straight away. A big water change will dilute any harmful substances very quickly.
To get 99.9% of the chemical out quickly, do a big (75-90%) water change and gravel clean the substrate every day for a week. Within a couple of big water changes and gravel cleans, you will remove virtually all of the chemical.
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The black algae on the rock looks like blue green algae (Cyanobacter bacteria).
Does this wipe off easily and smell musty?
If yes, it's blue green algae.
The black algae on the wood looks like black beard algae. It's a curse
Shrimp sometimes clean it up but it's one of the hardest algae to deal with.
