Acidic water is common in home water wells and can cause corrosion to piping, fixtures and appliances. Water that has a pH of less than 7.0 is considered to be acidic. The acid water pH can be neutralized to 7 or above by the use of an acid neutralizer tank, which allows calcium and magnesium carbonates to dissolve in the water. This eliminates the corrosive effect the water has on plumbing and fixtures.
For a pH of 6.0 to 6.9 a type of naturally occurring calcium carbonate media called Calcite is used to neutralize the pH. For water with a pH of less than 6.0, magnesium oxide is blended with Calcite to bring the pH to 7.0 or above. The Calcite or the blend of media is put in either an up-flow neutralizer tank or a down-flow neutralizer tank.
Acid neutralizer water systems are typically installed after the well pressure tank.
In down-flow neutralizer tanks the media flows from the top of the media inside a vertical filter tank down to the bottom of the tank, and up a distributor tube and out of the filter to the household piping. Down-flow neutralizer tanks also act as filters since sediment and other fine particles become trapped in the Calcite. This type of neutralizer is automatically or manually backwashed to keep the media clean.
In an upflow neutralizer the water flows down through the center distributor tube and enters the media bed at the bottom and flows up through the media before exiting the neutralizer and flowing out to the plumbing. Up-flow neutralizers do not get backwashed because the media is never compacted and no sediment is removed. Since the water is flowing up through the media the media is not compacted to theoretically it does not require backwashing.
There are advantages and disadvantages to both up-flow and down-flow neutralizers. The main advantage of the down-flow neutralizer is that it not only neutralizes the water, it also acts as a whole house sediment filter. Down-flow neutralizers are usually automatically backwashed, which cleans the Calcite media and prevents rust particles and other sediment from fouling or coating the media. Since additional Calcite or blended media must be added to most neutralizers once or twice a year, down-flow neutralizers are easier to backwash and put back in service than up-flow neutralizers which cannot be backwashed.
Up-flow neutralizers must use an internal top screen in to order to prevent the Calcite from entering the home plumbing system. Calcite has the appearance of white sand and can quickly damage valves and fixtures if the media enters the plumbing system. If the water contains iron, manganese or sulfides, these internal top screens can later become fouled and so are generally are not used for this reason. Instead of the internal top screen, a filter housing and cartridge filter are usually installed after the up-flow neutralizer tank to prevent any mineral from flowing into the plumbing system.
With down-flow neutralizers these upper screens or external filter housings are unnecessary since the Calcite is prevented from leaving the filter tank due to the bottom internal distributor screen. The bottom distributor does not get easily fouled due to the backwashing the down-flow neutralizer tank receives on a regular basis.
In filter tanks the media can flow around the media and create channels which allow the water to flow without properly contacting the media. This type of channeling is more of a problem with up-flow neutralizers and rarely happens with down-flow neutralizers due to the action of the backwash. For most residential applications down-flow neutralizers work better than up-flow neutralizers due to the filtration feature and the backwashing function.
A down-flow neutralizer can be backwashed on a regular basis to clean, re-classify and distribute the calcium media thoroughly. This backwashing allows the down-flow neutralizer to function properly and lower maintenance costs. The Calcite media dissolves better because it is cleaned and then compacted in the down-flow neutralizer tank.
Well water that is acidic can also sometimes be high in iron, manganese or hydrogen sulfide. If a greensand or other type of manganese media iron filter is used to treat the water for iron, the pH should be raised up to at least 6.8 to allow the iron filter media to work properly. A down-flow neutralizer is usually the best choice to put in front of an iron filter because the neutralizer acts as a pre-filter removing some oxidized iron prior to the iron filter. This lessens the load of iron that the greensand filter must treat. Iron, manganese and sulfides can coat the acid neutralizer media and render it unable to dissolve into the water and neutralize the pH.
There are some applications where up-flow Calcite neutralizers are more desirable than down-flow neutralizers. If the flow is more or less constant on a regular basis, such as when the neutralizer is used to fill a holding tank with neutralized water, the up-flow filter works fine. Since up-flow neutralizers have no automatic backwash control valve they are less expensive than down-flow neutralizers. If the water is of excellent quality with no sediment or iron and the flow rate is constant then the up-flow neutralizer costs less to use and uses no backwash water.