PURA NitrateLock 1L. Selective Ion Exchange Resin For Nitrate Removal. PURA NitrateLock rapidly removes and maintains extremely low to non-measurable levels of nitrates in fresh and salt-water aquariums. Long lasting, can be regenerated up to 24 times. Drastically reduces number of necessary water changes. Regeneration is accomplished with plain table salt, quick and completely safe. 1 L - treats 100 Gal tank for up to 24 months