What we test and why it matters
Every pool water testing visit in Madison, MS starts with a full panel, not a two-way strip. We measure free chlorine, combined chlorine, pH, total alkalinity, calcium hardness and cyanuric acid. On saltwater pools we also check salt level, and on any pool that is losing chlorine faster than it should we test for phosphates. Each of those numbers tells a different part of the story, and adjusting one without knowing the others is how pools end up with scale, etched plaster or a chlorine bill that makes no sense.
The reason we test on every visit rather than every few weeks is the climate. Central Mississippi pools in Ridgeland, Flowood and Brandon see hot water, heavy sun, high bather load on weekends and frequent rain from spring through fall. Any one of those can push chlorine or pH out of range within days.
- ■Free chlorine: 1 to 3 ppm (higher end in peak summer)
- ■Combined chlorine: under 0.5 ppm
- ■pH: 7.4 to 7.6
- ■Total alkalinity: 80 to 120 ppm
- ■Calcium hardness: 200 to 400 ppm
- ■Cyanuric acid: 30 to 50 ppm (60 to 80 ppm on saltwater)
- ■Phosphates: as low as practical, ideally under 100 ppb
- ■Salt (saltwater pools): per cell manufacturer, typically 2,700 to 3,400 ppm
Free chlorine, combined chlorine and what a chlorine smell really means
Free chlorine is the sanitizer that is actually available to kill bacteria and algae. Combined chlorine, or chloramines, is chlorine that has already reacted with sweat, sunscreen and other organics. Chloramines are what cause the sharp chlorine smell and eye irritation people associate with too much chlorine. In reality that smell almost always means there is not enough free chlorine and the pool needs to be shocked to break the chloramines apart.
We shock a pool when combined chlorine climbs above 0.5 ppm, after heavy use or after a big rain. The concept is breakpoint chlorination: raising free chlorine to roughly ten times the combined chlorine reading so the chloramines are oxidized completely. Shocking with a small dose that does not reach breakpoint just makes more chloramines. This is why we calculate shock dosing from the test instead of throwing in a bag and hoping.
In July and August, when water in Madison County pools runs in the upper 80s, we keep free chlorine toward 3 ppm because the demand is that much higher. A pool that tests fine at 1 ppm on a Tuesday can be at zero by Friday afternoon if a thunderstorm dumps debris into it.
pH and total alkalinity work together
pH controls how effective chlorine is. At 7.5, a good share of the free chlorine is in its active hypochlorous acid form. Let pH drift to 8.0 and most of it converts to the much weaker hypochlorite ion, so the same chlorine reading does far less work. High pH also scales tile and cloud water. Low pH is corrosive: it etches plaster, pits metal fittings and eats heater cores.
Total alkalinity is the buffer that keeps pH stable. When alkalinity is low, pH bounces every time it rains or a chemical is added. When it is high, pH creeps up constantly and takes a lot of acid to hold down. We set alkalinity in the 80 to 120 ppm range first, using sodium bicarbonate to raise it or muriatic acid to lower it, and then fine-tune pH. Adjusting them in the wrong order is a common mistake that wastes chemicals.
Fill water around Madison, Ridgeland and Gluckstadt tends to be moderate in alkalinity, but the amount of rainwater that ends up in an open pool during a wet spring can dilute the buffer and drop pH. We watch alkalinity closely after storms for that reason.
Calcium hardness and cyanuric acid
Calcium hardness protects the pool surface. Plaster, pebble and grout all contain calcium, and water that is too soft will dissolve it right out of the surface, leaving a rough, pitted finish. Water that is too hard leaves scale on tile, inside plumbing and on saltwater cell plates. We hold calcium between 200 and 400 ppm on plaster pools and toward the lower end on vinyl and fiberglass. Calcium does not evaporate, so it rises over time as water is topped off; the fix for very high calcium is a partial drain and refill, not a chemical.
Cyanuric acid, or stabilizer, protects chlorine from sunlight. Without it, direct Mississippi sun can burn off most of the free chlorine in a couple of hours. With too much, chlorine becomes slow and you need a higher free chlorine level to sanitize. Trichlor tablets add stabilizer with every dose, so a pool that runs on tablets all season will often test at 100 ppm or more of CYA by August. We track CYA monthly and mix in liquid chlorine or cal-hypo when it climbs, and recommend a partial drain when it gets out of hand.
Phosphates, metals and the problems chlorine alone will not fix
Phosphates are algae food. They come from lawn fertilizer that washes in with runoff, decaying leaves and pollen, some fill water and even certain scale inhibitors. A pool with high phosphates will hold chlorine on the test and still grow algae in the corners, because the algae are being fed faster than the sanitizer can keep up. When a pool in Flora or Canton with lots of trees keeps fighting us, phosphates are the first thing we check. A lanthanum-based phosphate remover drops them, and the filter needs a cleaning afterward because the removed phosphate ends up there.
Metals are the other hidden problem. Well water and some municipal supplies carry iron or copper, and copper can also come from a corroding heater or from algaecides. When chlorine is raised, dissolved metals oxidize and stain the plaster brown, green or black. A sequestering agent keeps them in solution, and we test for metals before shocking a pool that has a history of staining.
How the season changes what we do
Chemical balancing is not the same job in March as it is in July. In early spring the water is cool, chlorine demand is low and the main job is getting alkalinity, calcium and CYA set correctly for the season, while dealing with the yellow pollen that blankets everything in Madison County. Pollen is organic and burns chlorine, so we brush, skim and often run a clarifier to help the filter catch it.
By June the water is warm, kids are in the pool daily and sun is intense. Chlorine demand peaks, pH climbs from aeration and bather load, and we are adding acid and chlorine on most visits. After summer thunderstorms we test as soon as we can get to the pool, because a big rain drops pH and alkalinity and washes phosphates in.
September and October are about holding balance while the water cools and fewer people swim. Algae pressure eases, but leaves start falling and organic debris is the concern. A pool that goes into winter balanced comes out of it much easier in March.
Pool water testing and balancing as part of your service plan
Testing and balancing are included on every weekly and bi-weekly visit; there is no separate charge for the labor. Chemicals are billed at cost with no markup, and you see every reading and every dose on your visit report. That log matters. When a heater fails or plaster shows damage, having a season of documented chemistry protects you with the manufacturer and shows exactly what the water has been doing.
If you are handling your own pool water testing in Madison, MS and want a second opinion, or your pool is holding chlorine but still looks off, call 601-967-1717. We can run a full panel, explain what the numbers mean and tell you plainly what it will take to fix it.
Where we work
Pool Water Testing & Chemical Balancing is available across Madison County and the Jackson metro — Madison, Ridgeland, Gluckstadt, Canton, Flora, Flowood, Brandon, Jackson, Clinton, and Pearl.
Questions we get
How often should pool water be tested?+
At least weekly during the swim season in central Mississippi, and after any heavy rain, pool party or period of very hot weather. We test on every service visit.
Why does my pool smell like chlorine if the chlorine is low?+
That smell comes from chloramines, which form when chlorine is used up reacting with sweat and organics. It means the pool needs to be shocked to breakpoint, not that it has too much chlorine.
Do you use test strips?+
We use a liquid reagent test kit for the core readings and a digital photometer where precision matters. Strips are fine for a quick check but not accurate enough to dose chemicals from.
What is cyanuric acid and why do you care about it?+
It is the stabilizer that keeps sunlight from burning off chlorine. Too little and chlorine disappears in hours; too much and chlorine stops working well. We hold it between 30 and 50 ppm on most pools.
Is chemical balancing included in the monthly plan?+
Yes. Testing and balancing labor is part of every visit. Chemicals themselves are billed at cost.
Why does my chlorine disappear a day after I add it?+
Three reasons: sun with no stabilizer (cyanuric acid under 30), algae or organics eating it, or a pool full of kids and sunscreen. Test CYA first. Near zero, chlorine dies in two hours of Mississippi sun.
What happens when pH is too high?+
Chlorine gets weak; at pH 8 half of it is doing nothing. Calcium scales on tile and the salt cell and the water goes cloudy. Muriatic acid, a little at a time, in front of a return with the pump running.
Is chlorine lock real? I keep adding chlorine and it does not register.+
Mostly a myth. What people call chlorine lock is cyanuric acid over 100 from years of tabs; the chlorine is there but tied up. You cannot chemically fix it. Drain part of the water, refill, and get off tabs for a while.
How long after shocking can we swim?+
Wait until free chlorine drops under 5 ppm, usually 8 to 24 hours. Test it, do not guess. Non-chlorine shock is swim-safe in about 15 minutes.
Why is my pool foaming?+
Usually cheap algaecide or soap; sunscreen, lotion and a detergent-washed swimsuit foam too, and low calcium makes soft water that holds bubbles. Skip the foaming algaecide, check calcium, and let the skimmer clear it.