Acid neutralisers
The short answer
An acid neutraliser raises the pH of acidic well water, stopping it from dissolving copper out of your plumbing. The common type is a tank of calcite that the water passes through, dissolving a little limestone as it goes. It must be installed before any iron filter, because oxidising media barely works below pH 7.
- Where it goes
- Early — after sediment filtration, before any iron filter or softener.
- Typical cost
- $600–$1,800 installed for a calcite tank; more for soda ash injection
What it removes — and what it doesn't
This is the part sales pages are vaguest about, so it is worth being blunt. No single stage treats everything, and buying the wrong one for your water is the most common way people end up with expensive equipment that changes nothing.
Removes
- Acidity — raises pH toward neutral
- The cause of blue-green staining
- The corrosion that produces pinhole leaks in copper pipe
Does not remove
- Hardness — in fact calcite adds some
- Iron, manganese or sulfur
- Bacteria
- Copper already dissolved in the water (it stops the process, it does not filter the metal)
How the two types work
A calcite neutraliser is a tank filled with crushed limestone — calcium carbonate. Acidic water passing through dissolves a small amount of it, and that consumes the acidity. There is no power, no chemical to mix and no pump; the media is simply topped up as it is consumed. For most homes this is the right answer.
Where the pH is very low, or the flow rate is high, calcite alone cannot keep up: contact time is limited and there is a floor to how much it can raise pH in one pass. A soda ash injection system is used instead, dosing sodium carbonate solution into the line with a small metering pump. It is precise and can handle much lower pH, at the cost of needing power, solution mixing and regular attention.
A blend of calcite and a magnesium oxide media is a common middle path, raising pH further than calcite alone while staying passive.
The side effect worth planning for
A calcite neutraliser works by dissolving limestone into your water, and dissolved limestone is hardness. So the neutraliser raises your hardness as it does its job — often by several grains per gallon.
This matters in a specific and avoidable way. If you size a water softener before the neutraliser goes in, you will size it against the wrong hardness figure and end up with an undersized unit that regenerates too often. Fit the neutraliser first, retest, then size the softener.
It is also the reason a neutraliser and a softener are so often installed together. The neutraliser fixes the corrosion; the softener handles the hardness the neutraliser adds, along with what was already there.
Why it has to come before the iron filter
This is the single most consequential ordering rule in well water treatment, and it is routinely got wrong.
Iron filters work by oxidation — converting dissolved iron into particles a media bed can catch. That reaction is strongly pH-dependent, and below about pH 7 it barely proceeds. Manganese is worse still, needing pH above roughly 8 to oxidise reliably.
So an iron filter installed in acidic water underperforms from the moment it is commissioned. The water still has iron in it, the homeowner concludes the filter is faulty or undersized, and the usual response is to replace it with a bigger one — which has exactly the same problem. Fit the neutraliser first and the existing filter often starts working.
What it costs to keep running
A calcite tank is about as low-maintenance as water treatment gets. The media is consumed rather than exhausted, so it is topped up rather than replaced — typically a bag of calcite once or twice a year, depending on how acidic the water is and how much you use.
Most calcite units backwash periodically to prevent the bed compacting and channelling, which uses a modest amount of water and needs a drain connection. Every few years the bed benefits from being dumped and refilled rather than just topped up, because fines accumulate at the bottom.
Soda ash systems cost more to run: the pump uses power, the solution has to be mixed, and the injection point and check valve need periodic cleaning.
Cost figures are planning ranges for typical residential equipment, gathered from published pricing. They are not quotes, and installed cost varies widely with your plumbing, your water and your region. Get written quotes before committing.
Frequently asked questions
- Will an acid neutraliser make my water hard?
- A calcite one will add some hardness, because it works by dissolving limestone into the water. That is normal and expected. Size any water softener after the neutraliser is installed and the water retested, not before.
- Can I just use a water softener for acidic water?
- No. A softener exchanges hardness minerals for sodium and does not raise pH. Softened water is if anything marginally more aggressive toward copper. Low pH needs a neutraliser.
- How often do you add calcite to a neutraliser?
- Usually once or twice a year, though it depends on how acidic your water is and how much you use. The media is consumed as it neutralises, so the tank level falls gradually and is topped up rather than replaced.
- Does an acid neutraliser need electricity?
- A calcite tank with a simple backwashing valve needs a small amount for the control head; fully passive units need none. Soda ash injection systems do need power for the metering pump.