How dangerous is Melacure water to cats?

I just started using Melacure. I hope the smell alone is enough to deter them, but my cats love sticking their paws through the openings in the tank lid and they lick the water off their paws. I’m going to try covering the openings with screen material so there’s still airflow, but, I’m going out of town and very nervous it may not hold up. Has anyone dealt with this and what happened?