yeah thats what I used...erythromicin, but the name in the store will be Maracyn. But erythromicin is the active ingredient, or something like that. I got mine from Petsmart, from the Mardel company. the biggest pack that my store carried was an 8 pack but I needed 8 just for one dose...So I had to buy 5 pacages of 8...(it's 1 packet per 10 gallons for 5 days, I have 75g plus canister filters, so I averaged about 80 gallons...so 5 packages of 8). Five days later...no more cyno.
I've been up and down with people on this board about cynoBACTERIA not being 100% photosynthetic. But no one wants to believe that. But the prof is in the pudding as they say and after 4 days (3 were recommended) the Cyno (BGA) was so much worse than I had ever seen. And to clean my filters and find it growing on the inside of the canisters, where no light can exist...and yet the cyno is growing over everything...IT can NOT be due to light or no light.
I didn't want to have to use medicine. But I finally did and now it's gone. The meds themselves...are for "fin and tail rot, popeye, and body fungus", so I don't think it's going to HURT the fish...kind of like taking asprin even if you don't have a headache...so I don't think they'll die, but If you do have a hospital tank I would suggest using it for something like that. I DID NOT, and all mt cardinals and rummys were just fine and eating well...and the good news is that the lights are still on so that plants can still take advantage of the ferts...and they can beat back the BGA in their own way...more naturaly. My only problem now is the BBA...I think that's what the stringy stuff is...But I beat that back before and I think it's a side effect of the cyno leaving and the true algae having room to grow. My algae eaters are happy again though. I'll be looking forward to your updates and good luck with the blackout.