Aquarium Products Gel-Tek Erythromycin is a broad spectrum bacteriostatic antibiotic that exerts anti-bacteria action on susceptible organisms. It is effect against a number of Gram-positive and Gram-negative bacteria associated with fish diseases. Use for bacterial infections that cause cloudy or bulging eyes, swollen bodies and kidney infections. It can be used for gill disease, fin rot, wasting away and molly disease.