You are on the board of an HOA, a condo association, or a townhome community. Every week, a chemistry log appears in your portal. It has numbers for pH, free chlorine, total chlorine, alkalinity, calcium hardness, and cyanuric acid. Nobody on the board is a chemist. Nobody actually reads the log unless someone complains.
That is a problem, because those six numbers are what stand between your community and a closed pool, an unhappy membership, or — worst case — a health incident.
This article is the explanation we give to new board members who ask what any of this actually means. No chemistry textbook, no lecture. Just the six numbers, why each one matters, what happens when it drifts, and how to recognize when your pool management company is doing a good job.
Why chemistry matters at all
Water in a commercial pool is a chemistry system. Swimmers, sunlight, rain, dust, leaves, sunscreen, sweat, and the occasional toddler accident all change the water every single day. A properly operated pool holds a small number of key measurements inside tight ranges — and the result is clear water that kills germs and does not irritate skin or eyes.
When any of those measurements drifts outside its safe range, you get some combination of:
- Cloudy water
- Algae (green, yellow, or black)
- Red eyes, itchy skin, strong "chlorine" smell (this is usually a sign of too little chlorine, not too much — more on that below)
- Equipment corrosion or scale
- Illness outbreaks
- A citation from your county health department
- Closure
Every one of those is preventable, and every one of them comes back to one of the six numbers on the log.
The six numbers, in plain English
1. Free chlorine (1.0 – 5.0 ppm)
What it is: The active chlorine in the water that kills bacteria and viruses right now.
Why it matters: This is the sanitizer. No free chlorine means no killing power, which means bacteria, pink eye, ear infections, and the possibility of a cryptosporidium outbreak (which can close a pool for weeks). Too much free chlorine is uncomfortable but rarely dangerous at commercial levels — the code ceiling is 5.0 ppm.
Safe range: 1.0 – 5.0 ppm, with a practical target of 2.0 – 3.0 ppm for outdoor pools in the Chicago summer.
What drift looks like:
- Below 1.0 ppm: the pool is not sanitizing. Close it until chlorine is back up.
- Above 5.0 ppm: the pool will smell strongly, swimmers may get skin or eye irritation, and you are out of code range.
Who watches it: Every pool visit. Twice a day during operating hours is the minimum for Illinois.
2. Combined chlorine / chloramines (target: below 0.2 ppm)
What it is: Chlorine that has already reacted with contaminants (sweat, urine, organic matter) and is now worn out. It is still technically "chlorine," but it is not doing useful work anymore.
Why it matters: This is the single most misunderstood number in pool chemistry. When someone walks out of a pool complaining that "the chlorine is too strong" — it is the opposite. Chloramines are what cause the harsh smell, red eyes, and breathing discomfort. You fix them by adding more chlorine (shocking), not less.
Safe range: Below 0.2 ppm at all times. Code allows up to 0.4 ppm, but that is already a sign something is off.
What drift looks like:
- Above 0.2 ppm: strong chlorine smell on the deck, swimmer complaints, eye irritation. Shock the pool.
- Above 0.5 ppm: the pool should be closed until chloramines come down. This is usually a symptom of heavy bather load, a fecal incident, or under-dosing over several days.
Who watches it: Weekly full panel at minimum; daily on heavy-use pools during peak summer.
3. pH (7.2 – 7.8)
What it is: How acidic or basic the water is. 7.0 is neutral; below that is acidic, above is basic. Pool water targets slightly basic because that is where chlorine works and where skin is comfortable.
Why it matters: pH is the single fastest-drifting number. Swimmers push it up (sweat, urine, sunscreen), rain pushes it down (acid rain, especially in the Midwest), and even the chlorine feeder itself changes it. pH out of range does two bad things at once: it makes chlorine stop working, and it irritates swimmers directly.
Safe range: 7.2 – 7.8, with a target of 7.4 – 7.6.
What drift looks like:
- Below 7.2: metal corrosion, swimmer eye burn, chlorine becomes very harsh
- Above 7.8: chlorine becomes sluggish (even if the free chlorine number looks fine, it is not killing), scaling on tile and equipment
Who watches it: Every pool visit. In the Chicago summer, most commercial pools drift high and get acid-corrected weekly.
4. Total alkalinity (60 – 180 ppm)
What it is: The pool water's resistance to pH swings. Think of it as a shock absorber for the pH number.
Why it matters: Low alkalinity means pH bounces every time someone swims. High alkalinity means pH gets stuck and you fight it all season. Both cost money in chemicals and both leave swimmers uncomfortable.
Safe range: 60 – 180 ppm, practical target 80 – 120 ppm.
What drift looks like:
- Below 60: pH instability, chemistry fights, cloudy water
- Above 180: scaling on tile, calcium deposits, chlorine sluggishness
Who watches it: Weekly full panel. Alkalinity is corrected with baking soda (sodium bicarbonate) — a slow, multi-day process.
5. Calcium hardness (150 – 1,000 ppm)
What it is: The dissolved calcium in the pool water.
Why it matters: Too little calcium and the water actively pulls calcium out of your plaster, grout, and tile — slowly destroying the pool. Too much and calcium scales onto every surface, including the filter and heater.
Safe range: 150 – 1,000 ppm, with a target of 200 – 400 ppm for most plaster pools.
What drift looks like:
- Below 150: plaster etching, grout damage, tile falling off. This is a slow, expensive problem.
- Above 500: scaling, cloudy water, filter fouling, heater damage (heater tubes scale first)
Who watches it: Weekly full panel. Chicago tap water is already calcium-heavy, so most of our pools trend toward the high end and need occasional dilution with fresh water.
6. Cyanuric acid (0 – 100 ppm; practical cap 50 ppm)
What it is: The sunscreen for chlorine. It binds with chlorine and protects it from UV breakdown in outdoor pools.
Why it matters: Outdoor pools lose chlorine to UV light fast — without stabilizer, you are chasing chlorine all summer. But too much stabilizer and you reach "chlorine lock," where the chlorine reading looks fine but the sanitizing power is gone.
Safe range: 30 – 50 ppm for most outdoor commercial pools. Illinois allows up to 100 ppm, but most county inspectors will flag anything above 50 – 60 as a chlorine lock risk.
What drift looks like:
- Below 30: chlorine burns off in direct sun in a few hours
- Above 70: chlorine lock — you are dosing chlorine but the pool does not sanitize. Fix is to partially drain and refill, which is expensive.
Who watches it: Weekly. CYA only goes up unless you drain water — it does not "burn off" on its own.
How to read your weekly chemistry log like a board member
Most HOAs do not need their board to grade chemistry. They need the board to know what a normal log looks like and to spot trouble early. Here is the simple version.
Every week, look at:
- Is free chlorine between 1.0 and 5.0 on every reading? If yes, sanitizing is working.
- Is combined chlorine below 0.2 on every reading? If it trended up for 3+ days, something was missed.
- Is pH between 7.2 and 7.8? If it is drifting the same direction every week, the feeder is miscalibrated or the alkalinity is wrong.
- Are the weekly full-panel numbers stable (alkalinity, calcium, CYA)? If CYA creeps over 50 and stays there, ask about a partial drain.
Most boards we work with look at the log once a month — scroll through, check the trend lines, call or email if something drifts two weeks running. That is enough. The technician is already reading every number; the board's job is to make sure the technician is doing theirs.
Who is actually responsible
In Illinois, the Certified Pool Operator (CPO) on staff is the person legally accountable for the chemistry. That can be:
- A CPO employed by your pool management company (most common for HOAs)
- A CPO on your HOA maintenance staff (common for larger properties with a full-time building engineer)
- A contracted CPO who visits periodically
If you are an HOA board member and you cannot identify who the CPO on your property is, that is the first conversation to have with your pool management company. Without a CPO, you are not in compliance — regardless of how clean the water looks.
For the full compliance picture, see our IDPH commercial pool compliance checklist.
When should a board step in?
Three situations escalate from "the tech's job" to "the board's job":
- Multiple weeks of combined chlorine above 0.4 ppm. This is a systemic issue — either chronic under-dosing, a broken feeder, or a bather load the pool is not sized for. Ask for a root-cause report.
- Closures for chemistry. If your pool has been closed more than once in a season for chemistry reasons, that is not normal. Ask why.
- Member complaints of skin or eye irritation. If you are getting these and the chemistry log looks fine, the most likely culprit is combined chlorine (chloramines), not free chlorine. Ask about a shock.
In every other case, trust the CPO and read the log monthly. That is the working model for 200+ HOAs we serve.
Training your own staff
If your HOA wants someone on the property full-time who understands the six numbers — whether for backup, incident response, or cost savings — we run Certified Pool Operator (CPO) classes monthly at our Schaumburg office. The course is two days including the exam, covers all of the above plus regulatory compliance, and is the credential your IDPH inspector will expect to see posted at the facility.
Where to go from here
If your community wants professional weekly pool chemistry done right — logged, reported, and escalated when numbers drift — see our weekly pool maintenance service (or pick your own suburb from the Chicagoland coverage page) or request a written proposal. Our certified techs will handle the log, post it to your board portal, and call Chris directly the moment something is off.
