How much chlorine, salt and acid does your Pakenham pool actually need?
A standard local pool of 8m by 4m with an average depth of 1.5m holds 48,000 litres. Charging that from tap water to a 4,000 ppm salt target takes about 192kg, or ten 20kg bags at $16 to $22 each. One litre of 12.5 percent liquid chlorine lifts it by roughly 2.6 ppm, and one kilogram of stabiliser by about 21 ppm. Size your own pool with the estimator below and it will tell you the litres and the yearly chemical spend.
What this quantity estimate assumes
- Chemicals bought in bulk sizes once or twice a season, not 2kg tubs bought weekly. Small packs add $250 to $400 a year.
- A working filter and a pump turning the water over in 6 to 8 hours. A failing filter multiplies chemical use and nothing on this page fixes that.
- Pakenham mains water as the fill source, and a pool held between pH 7.2 and 7.6 with alkalinity in band.
- Excludes a green pool recovery, which is a separate one off job, and excludes equipment.
- A managed weekly chemical supply plan through a service route is a different product priced per week: see our pricing page.
How to measure your pool properly, with a tape and a phone
Volume is the number every dose depends on, so spend the ten minutes. Measure length and width at the water line rather than across the coping, because the coping overhangs and will add a few hundred litres of error. Then measure the depth at the shallow end and at the deep end, again at the water line, and average the two. Multiply length by width by average depth, then by 1,000, and you have litres.
Shape corrections are simple. A rectangle needs none. Multiply by 0.89 for an oval, by 0.85 for a kidney or freeform shape, and for a round pool use the diameter squared, times 0.785, times the average depth, times 1,000. If the pool has a wide beach entry or a deep diving well, measure those sections separately and add them, because averaging across them is what throws people out. Photograph each tape reading as you go so you never have to do it twice, and write the final figure on the inside of the pump lid in permanent marker. Every technician who ever works on that pool will thank you.
Not confident in your volume figure?
We measure and record it on the first visit, then every dose after that is calculated rather than guessed. First water test is free with any booked service.
The dosing rules of thumb worth memorising
All of these are for a 48,000 litre pool, so scale them up or down against your own figure. Salt: one kilogram per 1,000 litres lifts the level 1,000 parts per million, so a full charge to 4,000 ppm is 192kg and lifting an existing pool by 500 ppm takes 24kg, a bag and a bit. Liquid chlorine at 12.5 percent: one litre gives you about 2.6 ppm, so a 10 to 20 ppm shock is 4 to 8 litres. Granular chlorine at 65 to 70 percent: one kilogram gives about 14 ppm. Stabiliser: one kilogram gives about 21 ppm and the band you want is 30 to 50. Hydrochloric acid at 33 percent: roughly one litre pulls total alkalinity down by 15 to 20 ppm, though that varies with your starting chemistry, so add half, circulate, and retest before adding the rest.
Two habits make those numbers safe. Always add chemicals with the pump running so they disperse, and never mix them in a bucket. Add acid to water, never water to acid, and never add acid and chlorine anywhere near each other. If a dose is large, split it across two evenings rather than dumping it in one hit.
The wastage and safety allowance to add
Buy 10 to 15 percent more chlorine than the arithmetic says you need for summer. A run of 35 degree days in Pakenham can double chlorine demand for a week, and running short for two days in that weather is how a bloom starts. Keep one spare 20kg bag of salt and a kilogram of stabiliser in the shed so a weekend problem is not a Monday problem.
The opposite applies to liquid chlorine. It degrades, and a drum sitting in a hot Colorbond shed can lose a large part of its strength in a few months, so buy no more than six to eight weeks of it at a time and store it out of the sun. Granular chlorine and salt keep almost indefinitely if they stay dry, so those are the ones to buy in bulk. Acid keeps well but must be stored upright, away from metal and out of reach.
The sizing mistake that costs the most here
Over-estimating average depth. People remember the deep end and quote it as the depth, so a pool that really averages 1.5m gets treated as a 2m pool. That makes the volume figure a third too big, which means every single dose for years is a third too strong. Over dosing acid is the expensive version, because it drives alkalinity down and low alkalinity water goes hunting for calcium: that is what pits pebblecrete, etches a rendered interior and dulls tiles. Repairing an etched interior is a five figure job to save a few hundred dollars of measuring effort.
The second costly one is buying an undersized salt cell. Match a cell to at least 1.5 times the pool volume, so a 48,000 litre pool takes a cell rated to 70,000 or 80,000 litres. Undersized cells run 12 to 14 hours a day to make the same chlorine, which costs power and wears the plates out early. The third is a pump and filter that cannot turn the water over in 6 to 8 hours, which is covered in our pool pump selection guide. If you are still deciding between salt and manual dosing, the running costs of both are compared on salt versus chlorine in Pakenham.
A worked example on a typical Cardinia Lakes house
A rectangular pool measures 8.0m by 4.0m at the water line. The shallow end is 1.1m and the deep end is 1.9m, so the average depth is 1.5m. That is 8.0 times 4.0 times 1.5 times 1,000, which is 48,000 litres. It is a salt pool with no cover and a normal family swimming season from November to March. Here is the actual shopping list for a full year:
- Salt top ups, 4 bags at $16 to $22: $64 to $88 (the first fill charge of 192kg would be $160 to $220 on top)
- Liquid chlorine for heatwaves and after parties, about 60 litres: $135 to $195
- Hydrochloric acid, about 45 litres: $84 to $120
- Stabiliser, about 3kg: $34 to $45
- Clarifier and a mid summer algaecide: $45 to $70
- Phosphate remover once, if there is new lawn nearby: $55 to $90
- Test reagents or a refill of strips: $40 to $60
That totals roughly $460 to $670 for the year, which is where the estimator lands for the same inputs. Fit a cover and the chlorine and acid lines both fall by a third or more, taking the year closer to $320. The full cost comparison between doing this yourself and having it done sits on our budget pool maintenance guide.
The products you almost certainly do not need
Here is the part the chemical shelf will not tell you. A balanced pool with a working filter needs four things: a sanitiser, acid, stabiliser, and salt if it is a salt pool. Enzyme treatments, weekly clarifier, water conditioners and most of the multi purpose bottles are solving problems that a correct chlorine level and a clean filter already solved. If your chlorine demand keeps climbing, the answer is almost always a cover, a filter clean or a phosphate problem, not another product. And never buy anything to fix a number you have not measured: a $60 reagent test kit is more accurate than strips and pays for itself the first time it stops you dosing blind. If the water has already gone cloudy or green, start with cloudy pool water or algae shock in Pakenham rather than adding more of everything.
Want us to measure it and supply the right quantities?
Send your pool details and we will confirm the volume, the dose rates and a supply price within 1 business day.