When you've tried everything and those water spots won't budge, dry your eyes and reach for Viper Renew. Specifically designed for use on tile and grout which does not respond to other less venomous snakes, Viper Renew's safe, yet effective, acid-based formula will scare calcium carbonate clear off even the bravest of grout lines. Viper Renew will ambush efflorescence leaving no trace of it. It is biodegradable and emits less vapors than typical acid-based tile and grout cleaners.
Secondary use on tile and grout that does not respond to other cleaning agents.
Mix one-to-one with hot water.