Overview Product Description Tunze Osmolator Universal 3155 Auto Top Off is a reliable and safe automatic top-off (ATO) system that maintains steady water levels in aquariums using an electronic eye sensor and backup float switch sensor. Product Videos Custom Field Product Reviews Write a Review Write a Review × Icecap Bio-Plate 4" Rating * Select Rating 1 star (worst) 2 stars 3 stars (average) 4 stars 5 stars (best) Name Email * Review Subject * Comments *