i could not fix it no matter what i did, clean gravel, H2O2, blackout etc you name it, even Erythromycin was once failed to kill it, but am going to try Erythromycin one more time and hoping this will kill it.
I battled bga for 5 months and as we cant get Erythromycin here in scotland i had to find alternative solutions...in the end i used 2 doses of seacheams Potassium nitrate 1st day and 3rd day and the whole tank was cleared by the 5th day..I was amazed to say the least...it may work for other people as well...good luck
One of the reasons erythromycin works and the other 2920945+ antibiotics don't is because it is effective on gram positive bacteria. Your bio filter is safe. Just follow the directions and do the COMPLETE course as you normally would for a fish infection.