What do nitrates do to pool water?
Nitrates force sanitizers to do a lot more work, causing residuals to be more quickly depleted. As a result, more sanitizer will be needed and added time and money will be spent balancing pool chemistry levels. Even a small amount of nitrate, perhaps as little 10 ppm, can affect sanitizer demand. Higher amounts will wreak havoc on sanitizer levels; at 50 ppm, nitrates can more than double demand. The situation will become worse as nitrates accumulate.
Additionally, algae can become uncontrollable in the presence of a high nitrate supply, quickly making a mess of a pool. In fact, nitrates actually help algae grow, just as they do with plants and grasses in fertilizer form.
If nitrate levels fall below 10 ppm, algae should be controllable using regular methods. Above 10 ppm, routine algaecide additions may be needed to prevent an algae bloom and deal with added sanitizer demand. When nitrate levels rise above 30 ppm, algae can start to get out of control. Ideal free chlorine levels may even be ineffective in preventing algae when nitrate levels are this high.
The nitrate level also tends to be a big problem in the spring, when pools that have been closed all winter and opened for the first time. Any leaves, rain, organic debris or other material that have collected in the pool will likely have significantly increased nitrate nitrogen levels. It is always a good idea to test the nitrate level with the first test of every season, when the water level is already low and a partial drain and refill is less likely to interfere with weekend plans and pool parties.
How are these problems treated?
Knowing there is a nitrate issue is the first step in the battle. As such, levels should be tested any time an algae outbreak or increase in chlorine demand occurs. Test strips and test kits are available to perform this task and can easily become part of a regular troubleshooting maintenance routine.
Once identified, try to understand where the nitrates are coming from and prevent them from getting into the pool water. Prevention is the best approach, as treatment is difficult once nitrates are present.
The only practical way to lower nitrates once they have exceeded ideal levels is to drain and refill the pool with water that contains no or very low nitrate levels (ideally less than 1 ppm). In most cases, this can be accomplished with a partial drain and refill. Target nitrate levels should not exceed 10 ppm.
