Keep a small pool clean and safe for pets
Dog pools, paddling pools, and splash pads need sanitising too, but the doses on a bag sized for a 20,000-gallon swimming pool are wildly wrong for a few hundred gallons. This calculator scales standard chlorine and pH chemistry to your small pool’s volume and your test readings, returning gram-level doses.
How it works
Chlorine dosing uses a well-known reference: roughly 2 ounces of 65 percent calcium hypochlorite raises free chlorine by 1 ppm in 10,000 US gallons. The tool scales that linearly by your volume and the gap to the target:
ounces = ppm gap × (gallons ÷ 10000) × 2
grams = ounces × 28.35For pH it uses two reference rates: about 20 ounces of dry acid (sodium bisulfate) per 10,000 gallons lowers pH by roughly 0.2, while about 6 ounces of soda ash (sodium carbonate) per 10,000 gallons raises it by 0.2. The tool counts how many 0.2 steps separate your reading from the 7.4 target and scales the dose accordingly. Litres are converted to gallons first by multiplying by 0.264172.
Safe ranges at a glance
| Parameter | Safe range | Ideal target | Concern if outside range |
|---|---|---|---|
| Free chlorine (ppm) | 1 – 3 | 2 | Below 1: bacteria risk; above 3: eye/skin irritation |
| pH | 7.2 – 7.6 | 7.4 | Low pH: corrosive; high pH: chlorine becomes ineffective |
| Test frequency | Daily | Daily when in use | Small volumes change quickly, especially in sun |
Worked example
A 500-gallon dog pool with readings of 0 ppm chlorine and pH 7.8:
- To reach 2 ppm chlorine:
2 × (500 ÷ 10000) × 2 = 0.2 oz ≈ 5.7 gof 65% calcium hypochlorite (cal-hypo granules). - To lower pH from 7.8 to 7.4 (two 0.2-steps):
2 × 20 × (500 ÷ 10000) = 2 oz ≈ 56.7 gof dry acid (sodium bisulfate).
Add the chlorine first, wait 20 minutes with the pump running, then adjust pH. Test again before letting the dog back in.
Safety and practical tips
- Half-dose rule: small pools react quickly. Add half the calculated dose, circulate the water for 20–30 minutes, then retest and add the remainder if needed. It is much easier to add more than to dilute an overdose.
- Dissolve before adding: pre-dissolve granules in a bucket of pool water rather than adding them directly to the pool. Direct contact of undissolved granules with pool surfaces or pets can cause irritation or bleaching.
- Sunlight degrades chlorine: outdoor pools in direct sun lose free chlorine quickly. A stabiliser (cyanuric acid) extends chlorine life, but for dog pools you may prefer to simply treat daily and drain regularly rather than adding stabiliser.
- Drain and refill: for very small paddling pools (under 100 gallons), a complete drain-and-refill every 1–2 days is often simpler and safer than chemical maintenance, particularly when used heavily by multiple pets.
- Never dose while pets are present. Remove animals before adding any chemical and wait until the water has circulated and free chlorine has dropped to 3 ppm or below before allowing them back in.
These doses are estimates for fresh, moderately alkaline water. High total alkalinity or stabiliser levels change the chemical response. Always use a test kit, not just test strips, for accurate readings before dosing.