Antibiotics for cyanobacteria

	I recently treated my tank with 2.5mg/l of erythromycin to get 
rid of some cyanobacteria that were beginning to grow over my lileopsis. 
The treatment worked for a majority of the bacteria, but there are still 
a couple of small patches left after 4 days. Are there any other 
antibiotics that can be used against Gram negative bacteria that 
will not damage the plants or cause any other excessive harm? What I am 
really asking is whether anyone else has tried other antibiotics in a 
plant tank with better success rates. Thanks.