Magnesium Pool Maintenance: Weekly & Monthly Routine

Weekly routine: test, empty, brush, vacuum, top up

Test the water before completing the other weekly maintenance tasks. Use the results to assess pool conditions.

1. Test pH, chlorine and total alkalinity. Test strips are suitable for weekly checks. Use a liquid test kit when investigating a problem.
2. Empty the skimmer basket and the pump basket. Leaves in either basket restrict water flow and reduce turnover.
3. Brush the walls, steps and waterline. Grease collects at the waterline, and algae can develop there first.
4. Vacuum the floor, either manually or by running the cleaner for a full cycle.
5. Top up the water to the middle of the skimmer mouth. Use a hose filter if the fill water is hard or high in metals.

Use the following target values.

Reading	Target range	Ideal
pH	7.4–7.6	7.5
Total alkalinity	100–150 ppm	125 ppm
Chlorine	0.5 ppm	—
Bromine (if used instead of chlorine)	1 ppm	—
Calcium hardness — fibreglass and other shells (check at balance time, not weekly)	175–225 ppm	—
Calcium hardness — concrete or plaster shell (check at balance time, not weekly)	200–275 ppm	—

Maintain chlorine at 0.5 ppm in a magnesium pool. This is approximately half a standard chlorine pool's level. Do not use the chlorine target for a standard pool, because it is higher than the level intended for mineral water. If you use bromine instead of chlorine, maintain it at 1 ppm.

Correct total alkalinity first, followed by pH and calcium hardness. Total alkalinity buffers pH. If alkalinity is outside 100–150 ppm, a pH correction may need to be repeated. Calcium hardness changes more slowly than pH, so check it when balancing the pool instead of every week. Use a calcium hardness range of 175–225 ppm for fibreglass and other shell types, or 200–275 ppm for concrete or plaster.

Test the fill water. If its hardness is above 225 ppm, or above 275 ppm for a concrete or plaster pool, use a hose filter whenever you fill or top up the pool. A hose filter also removes copper, which can cause green staining.

Monthly: test salinity and top up the minerals

Test the salinity once a month. Add minerals when the salinity is below the required range. This is the main maintenance difference between magnesium and chlorine pools.

Minerals do not evaporate. They leave the pool through splash-out and backwashing. Adding fresh water also reduces the salinity. Pools with heavy summer use or frequent backwashing may require more frequent mineral top-ups. Most owners add minerals a few times per year rather than every month.

Minerals are sold in 25kg bags. The table shows the establishment dose required to raise the pool from its current salinity to the target range. You can also use it to calculate a top-up. Find the current salinity row and the pool volume column. The corresponding cell shows the required quantity.

Salinity	10,000L	20,000L	30,000L	40,000L	50,000L	60,000L	70,000L	80,000L
0 ppm	30 kg	60 kg	90 kg	120 kg	150 kg	180 kg	210 kg	240 kg
500 ppm	20 kg	40 kg	60 kg	80 kg	100 kg	120 kg	140 kg	160 kg
1000 ppm	20 kg	30 kg	50 kg	70 kg	90 kg	100 kg	120 kg	150 kg
1500 ppm	10 kg	20 kg	30 kg	40 kg	50 kg	60 kg	70 kg	80 kg
2000 ppm	10 kg	20 kg	30 kg	40 kg	50 kg	60 kg	70 kg	80 kg
2500–3500 ppm	½ bag	10 kg	15 kg	20 kg	25 kg	30 kg	35 kg	40 kg
4000 ppm	0 kg	0 kg	0 kg	10 kg	10 kg	20 kg	20 kg	20 kg
4500 ppm	0 kg	0 kg	0 kg	0 kg	0 kg	0 kg	0 kg	0 kg

Magnesium pools use one of three mineral delivery systems:

• Skimmer basket
• Floating dispenser
• In-line cartridge system connected to the return line

Add part of the required dose, run the pump to circulate the water, and retest the salinity. Add more minerals if required. Use the same staged dosing process used for chlorine.

The required mineral quantity depends on the pool volume. The 3m round Infinity 3 holds 6,275 litres, and the 4m Infinity 4 holds 10,410 litres. Establishing an Infinity 3 from 0 ppm requires approximately one 25kg bag. Establishing a 50,000-litre pool requires approximately six bags, or 150kg. These quantities apply to the initial establishment dose, not annual consumption. Later top-up quantities also increase with pool volume.

Filter, baskets and chlorinator care

Backwash the filter monthly, or sooner if the pressure gauge rises above its clean reading. After backwashing, run the rinse cycle before returning the valve to the filter setting. Skipping the rinse cycle can return dirty water to the pool.

A magnesium pool does not require a special filter. It uses the same pump, filter and plumbing as a chlorine pool.

Backwashing removes minerals from the pool. Salinity also decreases through splash-out and dilution from added fresh water. If you backwash two or three times in one month, a salinity test will usually show a low reading.

Most Australian mineral pools use a mineral chlorinator. It is similar to a saltwater chlorinator, but is configured for a magnesium-and-potassium blend instead of sodium chloride. It uses the dissolved minerals to generate the 0.5 ppm of chlorine in the water.

Inspect the baskets, chlorinator cell and filter media during the same maintenance check. Remove the lids, clean any scaled or clogged components, and reassemble them.

Seasonal and winter care

Reduce pump run times as the water cools. Maintain balanced water chemistry throughout the off-season. Cold water requires less sanitiser and circulation than summer water.

Seasonal changes do not affect the target ranges:

• pH: 7.4–7.6
• Alkalinity: 100–150 ppm
• Chlorine: 0.5 ppm
• Salinity: Use the dosing table.

Pools in South East Queensland are typically used less during winter. This reduces splash-out and slows mineral loss. Test salinity monthly throughout the year. Maintaining the correct salinity during winter helps prevent low levels at the start of summer.

Keep the pool cover on to reduce evaporation, prevent leaf litter from entering the skimmer, and retain heat.

Before summer, increase pump run times and resume weekly testing. Check salinity after periods of heavy swimming because splash-out removes minerals.

What a magnesium pool costs to run

A magnesium pool generally costs slightly more to run than a chlorine pool because of the mineral cost. Chlorine costs are lower because the water is maintained at 0.5 ppm instead of the level used in a chlorine pool.

The table uses figures from our dosing table and current bag prices. Establishment costs are one-off. After establishment, minerals are added as needed.

Line item	Basis	Estimate
Minerals	Per 25kg bag	$30–$60
Establishing a 6,275L Infinity 3 round plunge pool from 0 ppm	~1 × 25kg bag (one-off)	$30–$60
Establishing a 50,000L pool from 0 ppm	~6 × 25kg bags, 150kg (one-off)	$180–$360
Mineral top-ups	A few times a year; quantity set by the dosing table and your pool's volume	Bag price, pro rata
Chlorine	Held at 0.5 ppm, roughly half a chlorine pool's level	Lower than a chlorine pool's chlorine spend
Totals (one-off establishment)	6,275L plunge pool through 50,000L pool	$30–$360

There is no standard annual estimate for mineral use. Usage depends on pool use, backwashing frequency, and the amount of fresh water added. A heavily used pool that is backwashed most months uses minerals faster than a covered pool with light use.

Most owners add minerals a few times per year. The required amount is based on the salinity reading and pool volume. Establishment is the only mineral cost that can be estimated before installation, so it is the figure shown here.

With controlled dosing, the additional mineral cost and lower chlorine cost may offset each other compared with a chlorine pool.

Troubleshooting: cloudy, green and stained water

Cloudy water usually indicates a filtration or water balance problem rather than a mineral problem. Check that alkalinity is 100–150 ppm and pH is 7.4–7.6. Check the filter pressure and backwash the filter if the pressure has increased. If the water remains cloudy, increase the daily pump run time to improve circulation.

Green water indicates that chlorine has dropped below the 0.5 ppm target and algae is present. Brush the walls and waterline, correct the chlorine level, and run the filter continuously until the water clears. To continue Keeping a pool algae free, check the chlorine level weekly and brush the pool regularly. Focus on the waterline and rough surfaces behind the steps because an automatic cleaner may not reach them.

Green staining on the shell indicates copper rather than magnesium. Copper in the fill water can oxidise and stain the interior surface. Use a hose filter for every fill and top-up. Treat water already in the pool with a metal sequestrant.

FAQs

Are magnesium pools easy to maintain?

Yes. A magnesium pool requires the same maintenance as a standard pool, plus a monthly salinity test. The test shows whether the mineral level requires a top-up.

Continue brushing, vacuuming, emptying baskets, and backwashing as usual. No specialist tools are required. You need a test kit or test strips, a brush, a vacuum head, and pool minerals.

How much does it cost to maintain a magnesium pool?

A magnesium pool typically costs slightly more to maintain than a chlorine pool because it requires added minerals. Minerals are sold in 25kg bags, and most owners add them several times a year. The required amount depends on the pool volume and the dosing table. A round plunge pool requires less mineral than a 50,000-litre pool.

A magnesium pool maintains chlorine at 0.5 ppm, about half the level of a standard chlorine pool. This reduces chlorine costs. With careful management, the total maintenance costs of the two pool types can be similar.

How do you maintain a mineral pool?

Maintain a mineral pool in the same way as a magnesium pool. Magnesium chloride is the main mineral in the blend, and “mineral pool” is the trade name for this type of water. If your pool has a mineral chlorinator, it uses the dissolved minerals to sanitise the water. Keep the mineral level within the required range so the chlorinator can operate correctly.

Do you add salt to a magnesium pool?

Add mineral salts, not standard pool salt. Magnesium pools use magnesium chloride, often blended with potassium chloride. A salt water pool runs on sodium chloride, and a chlorine pool on dosed chlorine. Use the mineral blend specified for your pool when topping it up.

Can you put too much magnesium in a pool?

Yes. Add minerals in portions and retest the water after each addition. Do not add a full bag at once.

Swimming in a magnesium pool does not cause magnesium overdose. The body regulates magnesium levels and excretes excess magnesium.

Do you need to shower after swimming in a magnesium pool?

Showering after swimming in a magnesium pool is optional. Magnesium pools are sanitised at 0.5 ppm chlorine, roughly half the level used in a standard chlorine pool. Some owners rinse after swimming, but the water chemistry does not require it.

How long should you stay in a magnesium pool?

Stay in a magnesium pool for as long as you feel comfortable. There is no chemistry-based time limit. Consider the water temperature and your sun exposure, as you would in any pool.

What are the disadvantages of a magnesium pool?

The main disadvantage is cost. A magnesium pool costs slightly more to maintain than a chlorine pool because the minerals require ongoing replacement. Consider these costs as part of your buying decision.

---

Planning a new magnesium pool? Book a free site visit to determine the shell size, water volume, and dosing requirements for your block.