I have looked up the algae
Blue-green algae/Cyanobacteria
"Blue-green algae" is not really a true algae at all, but Cyanobacteria - a group of bacteria capable of photosynthesis. It can appear as a slimy coating in a number of different colours. It can smother plants and may release toxins harmful to fish. It can fix nitrogen and may therefore occur in tanks with zero or very low nitrates (but possibly high levels of other nutrients, particularly phosphate). It can be removed manually quite easily, as it often forms loose sheets, but it's likely to return quickly. Improving circulation/aeration in the tank sometimes causes it to decline. It can be treated with erythromycin (200mg/10 gallons) - this may however affect the filter bacteria, so it will be necessary to check for ammonia and nitrite after dosing.
seems like this, will this chemical mash up the fish???
Or is it best to take the fish out??
Dean
I have a fluval internal filter and have added extra airation yesterday