When taking water samples from testing, you should follow some basic practices. Be mindful that where you take a water sample from a pool is important. Sample location may not give a good idea of all the water in the pool. Various factors will determine where you take the sample:
Avoid corners and dead zones: Anywhere in the pool where water is not circulating freely. Corners, areas near stairs, etc.
Avoid return inlets: Do no take a sample near any returns. This will skew the test results heavily. The return is where you may have chemicals being put into the pool.
Do not take water from the surface: Always take a water sample 18 inches below the surface. A good rule of thumb is to submerge your arm up to your elbow. The water on the surface is not a good representation of the whole.
This image shows some examples of where you might expect lower or higher test results. Avoid these areas when taking a water sample.
Be aware that not every pool circulates the same. In a perfect world, your pool might be balanced between the skimmers/gutters and main drains, but often it is not. Here are a couple of examples of pools where the sample may be different than what the controller is seeing:
In a top balanced pool, seen above, an operator testing would see higher hand readings.
In a bottom balanced pool, seen above, an operator testing would see lower hand readings.
When comparing a reading to a chemistry controller, or preparing to calibrate the controller’s probes, the hand reading should always be taken from the sample port at the controller. This is the water the controller is seeing and may be different than the water in the pool.