Magnesium Pool Maintenance: Weekly & Monthly Routine
The full magnesium pool maintenance routine: weekly tests, monthly mineral top-ups, exact target ranges and run costs. Book a free site visit.
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Magnesium pool maintenance is the same weekly routine as any other pool, plus one extra check each month: the mineral level. Test pH, chlorine and total alkalinity weekly, test salinity monthly, and top up the minerals a few times a year.
A magnesium pool, also called a mineral pool, runs on dissolved magnesium chloride with a small supporting dose of chlorine at around half the level a standard chlorine pool carries. That lower chlorine target is the only difference in the day-to-day routine. Skimming, brushing, vacuuming and backwashing follow the fibreglass pool maintenance routine unchanged. The magnesium pool guide covers the background chemistry and the cost of building or converting a magnesium pool.
The magnesium pool maintenance schedule
The magnesium pool maintenance schedule sets five weekly tasks and three monthly tasks. Put the cover on every day the pool is not in use. Each season, adjust the pump run time to suit the water temperature while holding the chemistry in range.
| Task | Frequency |
|---|---|
| Test pH, chlorine and total alkalinity | Weekly |
| Empty the skimmer basket and pump basket | Weekly |
| Brush the walls, steps and waterline | Weekly |
| Vacuum the floor | Weekly |
| Top the water level back up to mid-skimmer | Weekly |
| Put the cover on | Every day the pool isn't in use |
| Test salinity (the mineral level) | Monthly |
| Top up minerals if salinity has dropped | Monthly, as needed |
| Backwash and rinse the filter | Monthly, or when pressure climbs |
| Wind pump run times back for the cold months | Seasonally |
| Hold the chemistry in range through the off-season | Seasonally |
Weekly routine: test, empty, brush, vacuum, top up
Start every week with the water test, because the four tasks that follow are easier to judge once the chemistry readings are known.
- Test pH, chlorine and total alkalinity. Strips are fine for a weekly check; a liquid test kit is more accurate if you're chasing a problem.
- Empty the skimmer basket and the pump basket. A basket full of leaves restricts flow to the pump, so the water turns over more slowly than the run time suggests.
- Brush the walls, the steps and the waterline. The waterline is where the greasy tide-mark forms and where algae takes hold first.
- Vacuum the floor, either manually or by letting the cleaner run a full cycle.
- Top the water level back to the middle of the skimmer mouth. Use a hose filter if your fill water is hard or high in metals.
These are the numbers you're testing against.
| 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 | — |
A magnesium pool holds chlorine at 0.5 ppm, roughly half a standard chlorine pool's level. Dosing a magnesium pool to a chlorine pool's target pushes the sanitiser above the level the mineral water is designed to run at. If you use bromine instead of chlorine, the target is 1 ppm.
Correct the readings in order: alkalinity first, then pH, then calcium hardness. Alkalinity buffers pH, so correcting pH while alkalinity sits outside 100–150 ppm means correcting the same pH reading again next week. Calcium hardness moves slowly compared with pH, so check calcium hardness when you are balancing the pool rather than every week. Check calcium hardness against the band for your shell: 175–225 ppm for a fibreglass shell and other shell types, and 200–275 ppm for concrete or plaster.
Fill water sets its own requirement. If your source water tests above 225 ppm hardness, or above 275 ppm for a concrete or plaster pool, run the hose through a filter every time you fill or top up. A hose filter also strips copper, which is the metal that causes green staining.
Monthly: test salinity and top up the minerals
Test the salinity level once a month and top up the minerals when salinity has dropped. That monthly salinity check is the whole difference between magnesium pool maintenance and chlorine pool maintenance.
Minerals do not evaporate. Minerals leave the water through splash-out, through backwashing and through the fresh water added on top, so a pool with heavy summer use and a couple of backwashes drops below range faster than a pool that sits covered. Most owners add minerals a few times a year rather than monthly.
Minerals are sold in 25kg bags. The table below gives the establishment dose, which is the one-off quantity that takes a pool from its current salinity up to range. The same table sizes a top-up: find your current salinity row, find your pool's volume column, and that cell gives the quantity the water is short.
| 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 |
There are three mineral delivery systems, and a magnesium pool runs one of them. Minerals enter the water through the skimmer basket, through a floating dispenser, or through an in-line cartridge system plumbed into the return line. Whichever system your pool uses, add a portion of the dose, let the pump circulate the water, then retest before adding more, which is the same discipline as dosing chlorine.
Pool volume multiplies every number in that table. Our 3m round plunge pool, the Infinity 3, holds 6,275 litres, and the 4m Infinity 4 holds 10,410 litres. Establishing an Infinity 3 from 0 ppm takes roughly a single 25kg bag, and establishing a 50,000-litre pool takes about six bags, or 150kg. That ratio applies to the one-off establishment dose rather than to annual consumption, and it sets the scale for later top-ups: the same salinity drop costs a small shell a fraction of what it costs a large one.
Filter, baskets and chlorinator care
Backwash the filter monthly, or sooner if the pressure gauge climbs above its clean reading. Backwash, then rinse, then return the valve to filter, because skipping the rinse cycle returns dirty water straight into the pool. A magnesium pool needs no special filter, and the same pump, filter and plumbing that ran a chlorine pool run a mineral pool unchanged.
Backwash water carries minerals out of the pool. Backwashing is therefore one of the three ways salinity drops, alongside splash-out and the fresh water added on top, so a month containing two or three backwashes usually returns a low salinity test.
Most Australian mineral pools run a mineral chlorinator. A mineral chlorinator is the same style of unit as a saltwater chlorinator, tuned for a magnesium-and-potassium blend rather than sodium chloride, and it generates the 0.5 ppm of chlorine the water carries from the dissolved minerals already present. Inspect the baskets, the cell and the filter media on the same walk-around: pull the lids, clean what has scaled or clogged, and reassemble.
Seasonal and winter care
Reduce the pump run times as the water cools, and keep the chemistry in range through the whole off-season, because a magnesium pool should not be left unbalanced over winter. Cold water requires less sanitiser and less circulation than summer water, so the pump run time comes down. The target ranges do not change with the season: pH stays at 7.4–7.6, alkalinity at 100–150 ppm, chlorine at 0.5 ppm, and salinity where the dosing table puts it, in July as much as in January.
Through a South East Queensland winter the pool is swum in less, which reduces splash-out and slows the rate at which minerals leave the water. Test salinity monthly regardless of season. The monthly salinity check is the one part of the routine that does not reduce over winter, because a pool that sits at the bottom of its salinity range all winter starts summer already short.
Keep the cover on. A cover reduces evaporation, keeps leaf litter out of the skimmer, and retains heat in a shell you are otherwise paying to warm.
Coming into summer the adjustments reverse. Extend the pump run times, return to genuinely weekly testing, and run a salinity check after any stretch of heavy swimming, because heavy swimming is when splash-out removes the most minerals.
What a magnesium pool costs to run
Running a magnesium pool costs slightly more than running a chlorine pool, and the gap is the minerals. The chlorine side of the bill moves the other way, because the water is held at 0.5 ppm rather than a full chlorine-pool dose.
The table below gives line items from our own dosing table and current bag prices rather than a quoted figure. Two of those line items are one-off, because the water is established once and topped up afterwards.
| 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 reliable annual bags-per-pool figure to quote. The rate at which a pool loses minerals depends on how heavily it is swum in, how often it is backwashed and how much fresh water is added on top, so a heavily used pool backwashed most months consumes minerals faster than a covered pool in light use. The pattern of the spend holds across both cases: most owners top up a few times a year, and the dosing table sizes each purchase from the salinity reading and the pool's volume. Establishment is the only mineral cost that carries a firm number before the pool is in the ground, which is why establishment is the figure quoted here.
Where owners manage the chemistry tightly and rarely over-dose, the extra mineral spend and the reduced chlorine spend can offset each other against a chlorine pool.
Troubleshooting: cloudy, green and stained water
Cloudy water is usually a filtration or balance problem, not a mineral problem. Check that alkalinity is inside 100–150 ppm and pH inside 7.4–7.6, then check the filter pressure and backwash if it has climbed. Cloudiness that persists after both checks is normally caused by under-circulation, so extend the daily pump run time.
Green water means chlorine has fallen below the 0.5 ppm target and algae has taken hold. Brush the walls and waterline hard, correct the chlorine level, and run the filter continuously until the water clears. Keeping a pool algae free afterwards requires the weekly chlorine reading and the brushing step, because algae colonises the waterline and the rough surfaces behind the steps first, and a brush reaches those surfaces where an automatic cleaner does not.
Green staining on the shell is copper, not magnesium. High copper in the fill water oxidises and marks the interior surface. Fix the input with a hose filter on every fill and top-up, and treat the water already in the pool with a metal sequestrant.
FAQs
Are magnesium pools easy to maintain?
Yes, and the reason is that a magnesium pool adds one task to a standard pool routine rather than replacing it. The added task is a monthly salinity test, which tells you whether the mineral level has dropped far enough to need a top-up. Nothing about the mineral water changes how you brush, vacuum, empty baskets or backwash, and no part of the routine requires a specialist tool. A test kit or test strips, a brush, a vacuum head and a bag of minerals cover the whole routine.
How much does it cost to maintain a magnesium pool?
A magnesium pool costs slightly more to maintain than a chlorine pool, and the minerals account for the difference. Minerals are sold by the 25kg bag, and most owners top up a few times a year. The exact quantity comes off the dosing table for the pool's volume, so a round plunge pool costs a fraction of what a 50,000-litre pool costs to keep in range. The chlorine spend moves the other way, because a magnesium pool holds chlorine at 0.5 ppm, about half a standard chlorine pool's level. Tightly managed, the two pool types can cost close to the same amount to run.
How do you maintain a mineral pool?
A mineral pool is maintained exactly as a magnesium pool is, because magnesium chloride is the main mineral in the blend and "mineral pool" is the trade name for the same water. If your pool came with a mineral chlorinator, that unit is doing the sanitising work off the dissolved minerals, and your job is to keep the mineral level within range so it has something to work with.
Do you add salt to a magnesium pool?
You add mineral salts, not ordinary pool salt. A magnesium pool runs on magnesium chloride, usually blended with potassium chloride; a salt water pool runs on sodium chloride, and a chlorine pool on dosed chlorine. Tipping pool salt into a magnesium pool pushes the water back towards saltwater chemistry, so top up with the mineral blend the pool was established on.
Can you put too much magnesium in a pool?
You can over-dose the water, which is why you add minerals in portions and retest between them rather than tipping in a full bag. For swimmers, there is no equivalent risk: magnesium levels are regulated by the body and any excess is excreted, so there is no such thing as overdosing on magnesium from swimming.
Do you need to shower after swimming in a magnesium pool?
Showering after a swim is personal preference rather than a chemical necessity. A magnesium pool is sanitised at 0.5 ppm chlorine, roughly half a standard chlorine pool's level. Plenty of owners rinse anyway out of habit, and nothing in the water chemistry requires it either way.
How long should you stay in a magnesium pool?
Stay in a magnesium pool as long as you are comfortable. A magnesium pool carries no chemistry-based time limit. The practical limits are water temperature and sun exposure, as they are in any pool.
What are the disadvantages of a magnesium pool?
The disadvantage that shows up in the maintenance routine is cost. Running a magnesium pool costs slightly more than running a chlorine pool, because the minerals are an ongoing purchase. The full set of magnesium pool drawbacks is set out with the rest of the buying decision.
Planning a new pool and want it running on magnesium from its first fill? Book a free site visit and we'll size the shell, the volume and the dosing for your block.
