Pool Chlorine Cost Calculator —
Liquid vs Tablets vs Cal-Hypo
Compare the true seasonal cost of each chlorine type — including the hidden CYA drain cost that makes trichlor tablets more expensive than they appear.
Trichlor drain cost assumes a 62% drain to reset CYA from 80 ppm back to 30 ppm, plus $30 for re-balancing chemicals per drain event. Water cost uses the rate entered above. Demand, prices, and drain timing are estimates — actual costs vary by region and pool conditions.
The hidden cost most guides miss
Trichlor tablets are 54% cyanuric acid (CYA) by weight. Every tablet raises CYA slightly. CYA never dissipates — the only way out is draining and refilling water. At typical usage, CYA reaches the 80 ppm limit within 7–10 weeks, requiring a partial drain that costs $65–200 in water plus $20–40 to re-balance chemicals. Repeat that two or three times per season and the "cheaper" tablets become the most expensive option.
Why trichlor tablets cost more than they appear
Trichlor (trichloroisocyanuric acid) is about 54% cyanuric acid by molecular weight. When it dissolves, the chlorine does its job and the cyanurate ring stays in the water permanently. Most pool chlorine cost guides calculate only the sticker price of the tablets — they skip the drain.
At a typical weekly FC demand of 10 ppm/week, trichlor adds roughly 6 ppm of CYA per week. Starting from CYA 30 ppm, you hit the 80 ppm threshold in about 8 weeks. Resetting to 30 ppm means draining about 62% of the pool. In a 15,000-gallon pool at average water rates, that's $65–200 in water cost plus re-balancing chemicals — and the cycle repeats two or three times per season.
Liquid chlorine adds no CYA and no calcium
Sodium hypochlorite is the cleanest long-term option for most pools. It adds only available chlorine and water. For pools that already have high CYA from past tablet use, switching to liquid chlorine stops the accumulation immediately — no drain required just to switch products.
Cal-hypo: the middle option
Calcium hypochlorite adds no CYA, making it much better than trichlor for long-term use. The trade-off is calcium: every dose slightly raises calcium hardness (CH). In pools where CH is already high — especially in regions with hard fill water — repeated cal-hypo use can push CH above 400 ppm, which causes scaling on surfaces, tile, and equipment. If your source water is soft (CH below 150 ppm), cal-hypo can be an excellent and cost-effective choice.
Frequently asked questions
Is liquid chlorine cheaper than trichlor tablets?
Often yes, once CYA drain costs are factored in. Trichlor tablets frequently appear cheaper by $1–3 per week on chemical cost alone, but each partial drain to reset CYA adds $80–200 in water and re-balancing costs. Over a 20-week season, two or three drains typically erase the apparent savings.
How much does it cost to maintain a pool per month?
For a typical 15,000-gallon pool using 12.5% liquid chlorine at $5/gallon with moderate demand (10 ppm/week), expect roughly $23–30/month in chlorine during swim season. Trichlor tablets may look like $20–25/month but the true cost including partial drains is typically $50–80/month when amortized across the season.
Why do trichlor tablets force partial drains?
Trichlor is trichloroisocyanuric acid — 54% cyanuric acid by molecular weight. When the chlorine portion does its job, the CYA ring stays in the water permanently. CYA does not evaporate, break down, or leave the pool on its own. Once it exceeds 80 ppm, your minimum FC target rises proportionally, algae risk increases, and a partial drain is the only fix.
Can I mix chlorine types during a season?
Yes. You can switch between liquid chlorine, trichlor, and cal-hypo at any point — each produces the same active disinfectant (hypochlorous acid) once dissolved. If switching away from trichlor, test CYA first — you may already be close to the drain threshold.
What is the cheapest way to chlorinate a pool?
For most residential pools, 12.5% liquid chlorine purchased locally in bulk is the most cost-effective long-term option — no CYA buildup, no calcium accumulation, and widely available. Cal-hypo at low bulk prices can match or beat liquid chlorine if your calcium hardness is on the lower side. Trichlor tablets are rarely the cheapest option once CYA drain costs are included, despite having a lower sticker price per unit of chlorine.
Track chlorine cost alongside your chemistry.
PoolChem Tracker logs every reading and dose, tracks CYA trends over time, and tells you exactly when to add chlorine — so you never over-dose or let FC slip.
