The Hanna HI721 Iron Checker gives quick accuate results for the price of a chemical test kit. About 6.3% of the earth crust is made of iron with 43% of this amount held in the soil. As a result, iron is naturally present in most water supplies. Left in the water, iron will not only stain pipework and swimming pool surfaces it will also affect the water taste and cause problems with animal feed lines. Testing should therefore form an important part of any water monitoring process ? particularly if you are checking your pool, watching the quality of water in your fish tank or needing to monitor water run-off.