Water Chemistry /
What Chemistry Checks Matter Most Before Opening a Pool?
Before opening a pool, focus on the chemistry checks that protect swimmers and equipment: sanitizer, pH, alkalinity, calcium hardness, and stabilizer.
Archive date: this article was written for PoolSkimmer on Oct 7, 2026 and given the earlier archive date of Oct 9, 2025 so the blog reads as an organized archive. It was not published on that date.
Begin with a safe inspection
The first step in opening a pool is to put on some suitable PPE and have a look at the water and equipment. Clear away any debris you can see, examine the cover, and note if the water has turned green or cloudy, or has an unpleasant odour. Should you have any reason to think there is an electrical issue, do not enter the water. Before you go near any strainer parts or open the skimmer basket, shut off the pump and refer to the chemical labels and manuals for guidance.
Do not be fooled by appearances when deciding if the pool is ready; rely on the numbers from a good test kit or fresh strips instead.
What to check in the water
Sanitizer should be your top concern as it is what keeps algae and bacteria in check. A pool can appear perfectly fine yet be unsafe if sanitizer is absent or running low. After that, give the pH some attention. It is a factor in swimmer comfort and how well the sanitizer does its job, and high or low levels can be hard on the eyes and surfaces.
You will also want to monitor total alkalinity to prevent the pH from fluctuating too quickly. Unstable alkalinity can lead to drift and make it difficult to get the water in balance once the pool is open. Then there is calcium hardness, which is there to protect your plaster, grout, tile and heaters from being too soft and aggressive or developing scale from water that is overly hard. For those with stabilized chlorine, a check of the cyanuric acid is in order since sunlight will otherwise diminish the life of your sanitizer.
An orderly way to open
There is merit in following a straightforward sequence so one problem does not create another:
- Have a thorough look at the pool and the equipment zone
- With the pump off, clean out the baskets and take care of debris
- Run your tests for stabilizer, calcium hardness, alkalinity, pH and sanitizer
- See how the results stack up against the manual and kit instructions
- Circulate and retest after making a single correction
This approach minimizes errors and lets you tell what is actually working. It is better than trying to fix everything in one go or putting products in haphazardly.
When to leave it to the professionals
It is all too easy to want to jump in because the pool “looks close enough,” but resist the urge. Do not mix chemicals unless the label instructs you to, and never put your hands in suction equipment while it is running. One quick test is not enough to go on.
If the water will not clear up or readings refuse to hold after you have done your part, or if you are faced with staining, corrosion, a leak or any trouble with the automation, heater or filter, it is time to call a qualified pro. This is particularly true where you suspect an electrical fault or are unsure of the water quality. Wait until the system is safe and the water is properly balanced before you swim.