I agree with SCF there is no harm what so ever. in fact they sell a water crystal mixture at petco and other pet stores for an outrageous prices when you can get dried crystals that you just add water to for a price that is 100 times less. yeah petco has calcium enriched crystals but just give your feeders Romain lettuce and you will deliver much more calcium to your feeder then what you can get out of the zoo med brand. Saves you much more money.