Acid Neutralizer Sizing Guide: What Size Do You Need?

A caller in Louisiana had just drilled a new well and his tub was turning blue-green. He wanted the smallest tank I sell, a two-bag neutralizer, because it is just him and his wife in a two-bedroom house. I told him no, that is too small. A two-bag tank is for water that is already close to neutral with very little use. He had not tested his pH yet, three daughters come and go, and for $300 more than the two-bag tank, the 2.5 cubic foot tank holds five bags instead of two. That is the whole sizing conversation, and this page is the long version of it.

Your pH decides the size first

pH is the number one thing I look at when I size a neutralizer. Plain calcite handles water down to 5.5 in a 2.0 or 2.5 cubic foot tank. In the smaller 1.0 and 1.5 it handles water down to 6.0. The lower the pH, the more limestone the water has to touch on its way through, so the more acidic the water, the bigger the tank and the more calcite I want in it.

Most acidic wells are not that acidic. Of the acidic wells my customers have had lab-tested, about four in five came back between 6.0 and 6.9. That is the range where any size I sell works with plain calcite. About one in five was in the 5s, and only one was below 5.5. So for most people reading this, pH is not what pushes them to the 2.5; the fixtures running at once and the years between bags do that.

Below 6.0 the size matters more. A caller in North Carolina had strips reading five and a half to six, three people and two baths, and had settled on a 2.0 "for longevity." At 5.5 I want the 2.5. It does a better job of holding the pH up at neutral while water is running, and the 1.5 is out of the question at that level. Below 5.5 I add FloMag (a magnesium mineral that dissolves faster than calcite) to the calcite. A family in Alabama with a pH of 4.8, five people in a 1,200 square foot trailer, got the 2.5 with FloMag mixed in, and that water comes out between 7 and 8. How many pounds go in depends on your number, so if you are below 5.5, text me the pH.

On the small tanks the line moves up: a 1.0 or 1.5 gets FloMag from 6.0 down, because it holds two or three bags instead of five.

Before you pick a size

Don't know your pH yet?

You need the pH number before you can size the tank. The certified lab test, mailed to you, run by an accredited lab, gives the exact pH plus hardness, iron and copper from one sample. Already have a pH? Skip this.

See the certified well water test ($199)

53 contaminants. Results reviewed by Aidan, in plain English. On city water, use the city water test.

Do more people mean a bigger tank?

A little. What matters is not how many people live there but how many showers and faucets can run at the same time, and how fast the calcite gets used up. If two people and a pH of 6 is the house, the 1.5 does it. If six to eight people and a pH of 5.5 is the house, order the 2.5. Those are the two examples I give in the video, and most homes fall between them.

The reason the count of people matters less than you would think is that the tank only works when water is moving through it. When nothing is running, the water inside sits at neutral and stops dissolving calcite. A second home in New York with a pH of 6.11, two people most weekends and four or five on holidays, could take any size from the 1.5 to the 2.5. What the bigger tank buys that family is flow: with two showers and the dishwasher going, the 2.5 does not give you the pressure drop a 1.5 can. I told a New Jersey caller the same thing. Just the pH level; it does not really matter how many people live in the house for the most part, but a 2.5 does not have that big pressure drop when two fixtures run at once.

Bathrooms are my shorthand for that. Three baths in a house means three showers can run together, and I want the tank that handles it.

Three and a half minutes with the three tanks in front of me: which one for which pH and household, when the 1.5 is the right buy, how often each one needs a bag, and why flow rate does not matter on a non-backwashing tank.

When the 1.5 is the right size

The 1.5 is the right tank when the pH is in the mid-6s and it is one or two people, or when the only spot you have fits a 10-inch tank. It is not a budget compromise. It is a smaller tank for a smaller job.

A caller in Illinois, just him and his wife, one bathroom, pH between 6.5 and 6.8 depending on the day: that is a 1.5 with plain calcite. A caller in Connecticut had a 1.5 backwashing tank he wanted to replace with a non-backwashing one. He would have loved the 2.5, but his spot is boxed in by the well line, the pressure tank, the electric panel and an oil heater, and his tank is 10 inches across where the 2.5 is 13. He measured 54 and a quarter inches to the top of the tank with about four inches of valve above it. The 12 x 52 tank (the 2.0) was the other option, but he was good at the 1.5, and I told him so.

Two things to know if space is what puts you in the 1.5. First, at the same pH the smaller tank gets FloMag sooner: from 6.0 down instead of 5.5. Second, you will add a bag more often, every 18 to 24 months instead of 30 to 36.

Ask Aidan

Text me your pH number

Send the pH, how many people, how many bathrooms, and the height and width of the spot. I will tell you which size, whether it needs FloMag, and how many pounds go in each bag.

Text Aidan 443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, usually Aidan.

Every size, with the measurements

There are four non-backwashing sizes and three backwashing ones. Measure your space against the installed height, which includes the valve on top. The tank sizes below are diameter by height in inches. The valve adds a few inches, and the installed height is the number to hold up against your ceiling.

Prices are shipped, with the calcite in separate bags to load at install (two bags for the 1.0, three for the 1.5, four for the 2.0, five for the 2.5) and the bypass valve already on the control valve. Add $200 to any size for the FloMag blend. The refill column is the average for plain calcite; very low pH shortens it. The Alabama family at 4.8 will add a bag to their 2.5 every 18 to 24 months, not every 30 to 36, and a weekend house stretches it the other way. You check the level once a year with a flashlight against the back of the tank, and add a bag when it is about halfway down. How to add calcite, step by step.

Non-backwashing or backwashing does not change the size. They raise the pH the same way; the valve on top only decides whether the tank rinses itself. About nine of every ten tanks I sell are non-backwashing, and the backwashing valve is for water with iron or heavy sediment that would pack the calcite. Backwashing vs non-backwashing, in full.

Does flow rate or pump size matter?

Flow rate doesn't matter when you're using a non-backwashing acid neutralizer. A backwashing tank does need flow: 5 to 7 gallons per minute for a 2.5, closer to 15 for a 3.5. I get that question all the time on the phone and by text, so I will say it twice: on a non-backwashing tank, your well pump's gallons per minute has nothing to do with which size you buy. (In the video I say 5 gallons a minute for the backwashing 2.5; the product page lists 7 to leave a margin. Almost any working well pump delivers that.)

A caller in Ohio with a 7 gallon per minute well worried that was not enough for a backwashing 2.5. It is. The only tank that asks a lot of a pump is the 3.5, which wants upwards of 15 gallons per minute, and that is a light commercial unit.

What a bigger non-backwashing tank does change is pressure drop. With two showers running you do not get the drop you can get through a 1.5, and none of these tanks cuts your water pressure the way an old gravel-bed tank can. One buyer of the 2.0 wrote that his pressure was back to what it was with his old neutralizer bypassed.

Can I go too big?

No. With a neutralizer, bigger is better. Sizing up gives you more calcite capacity and longer intervals between maintenance. The water spends more time against the calcite and you add a bag less often. That is why the 2.5 is the tank most people end up with: of the neutralizers ordered from me this year, about eight of every ten were the 2.5 and one in ten the 1.5.

Going bigger costs you three inches across and $100 or $200. It does not push the pH too high. Calcite stops dissolving once the water is neutral, so a 2.5 on mildly acidic water comes out neutral, the same as a 1.5 would.

What buyers of each size saw

Here is what buyers of each size reported for pH before and after, in their own words. Two of them did not get all the way to neutral, and both are the kind of water the pH section above says needs the 2.5 or the FloMag blend. The reviews are verified purchases; names appear as the buyers wrote them.

Frequently asked questions