Aquarium Products Gel-Tek Tetracycline 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 gill disease, bacterial tail rot and infections, ulcers, sores, dropsy, pop-eye, Columnaris, Aeromonas, Pseudomonas, and Chondococcus.