Carefully collect and care for the water sample.
When approaching a 20,000-gallon pool to collect a testing sample, it’s easy to fall into the trap of thinking that the water on one end is the same as the water on the other. Or, that the water near the surface is chemically identical to the water down deeper. Don’t make this mistake.
Before you even get to the testing, the sampling technique and sample handling are big factors, you want to get a sample that’s representative of the whole body of water so you’re not taking in a sample that’s higher or lower in chlorine, for example, than the rest of the pool.
So where is this water? You’re not going to find it near the top step, nor are you likely to find it by randomly dipping a vial into the water. Your best bet, experts say, is at least a foot deep, midway between the shallow and deep end, away from return lines and skimmers. In addition, if the water’s been treated recently, make sure it’s turned over a couple of times.
This water should be collected in a clean vessel that’s been rinsed with the water you’re about to collect. The goal here is to avoid cross contamination.
Use a clean plastic bottle. Insert it bottom-side up so the trapped air keeps out the water momentarily. Turn the bottle rightside up when you get to elbow depth and let it fill.