Aquarium Products Gel-Tek Neomycin is a broad spectrum bacteriostatic antibiotic that exerts anti-bacteria action on susceptible organisms. It is mainly effective against a number of Gram-positive bacteria but has demonstrated activity against Gram-negative bacteria associated with fish diseases. Use for bacterial infections that cause ulcers, sores, swelling body and fin rot. It is also effective against secondary infections from gourami and neon tetra diseases, loss of color, and furunculosis.