Does Maracyn 1 & 2 kill beneficial bacteria?

Question

I've used the meds before in smaller tanks and have never had a problem with it, but I need to make sure that the meds won't be killing the beneficial bacteria.

I'm going to have to use some in our 28gal tank b/c I think some kind of bacterial infection is spreading. I rely on this tank for the extra filter media (for my other tanks when I need to replace what they have)... so yeah... I need to either make sure nothing is going to happen, or plan on using one of the other tanks as a temporary replacement for that.

Answer 1

Yes, it can disrupt the nitrogen cycle in your tank.  If that's the tank that is infected, you should probably treat the entire tank and not use it's filter media for other tanks until you're sure the bacterial infection is gone.  You should never use filter media from an infected tank with another tank.  

Test your water often and watch the ammonia and nitrite levles while treating.

Answer 2

Yes, I'm afraid so.  Maracyn and Maracyn II are antibiotics, so they kill bacteria.  That includes the bacteria that "cycles" your tank.  When treating sick fish with these medications it's always best to use a seperate hospital tank whenever possible.  I'm sorry.  If you have another tank or tanks,  finish the course of meds in this one, run some carbon through the filter to remove the medication from the water and then put some gravel from your other tanks into this one to kickstart your tank's re-cycling.