A chemical injection tank is the solution tank in a well treatment system: the vessel holding the diluted chlorine, peroxide or soda ash that a metering pump feeds into your water line. Getting it right is mostly about batch strength, tank size and siting, because a solution that is too strong, too old or too far from the pump makes an otherwise sound system dose erratically or stop dosing altogether.
What the tank does, and the parts around it
An injection system has four pieces working together. The solution tank holds the diluted chemical. The metering pump draws from it through a foot valve and strainer and pushes a measured dose into the line, usually switched with the well pump or paced by a flow meter. The injection point, a fitting with a check valve, admits the dose to the pipe, and a static mixer or a length of pipe blends it. A retention tank downstream then gives the chemical the contact time it needs before a filter removes what it created. The solution tank is the simplest of these and the one that most often causes trouble.
Sizing the tank and mixing a batch
Size the tank so a batch lasts a comfortable refill interval, typically weeks rather than days, since a tank you must top up constantly will eventually be forgotten. Bigger tanks also mean a weaker, more dilute solution for the same dose, which is easier on the pump and safer to handle. Mix by volume with a marked container, label the tank with the date and strength, and keep a written note of the recipe so anyone can repeat it. Chlorine solutions lose strength over time, so smaller, fresher batches dose more consistently than one enormous batch that weakens week by week.
Siting the tank safely
The tank belongs somewhere dry, frost free, ventilated and out of direct sunlight, which degrades chlorine quickly and encourages growth in translucent vessels. Put it on a level, chemically resistant surface, ideally inside secondary containment such as a tray or drum liner that would hold the contents if the tank split. Keep it away from electrical panels and anything corrodible, and keep the lid on: an open tank invites debris, evaporation and curious hands. Keep the pump close to and slightly above or below the tank per the pump's instructions, because long suction lines are the classic cause of lost prime.
The retention tank is not the solution tank
These two get confused constantly, and the difference matters. The solution tank is an unpressurized vessel of diluted chemical sitting beside the pump. The retention tank is a pressure vessel plumbed into the water line after the injection point, whose only job is to hold treated water long enough for the oxidant to work on iron, sulfur or bacteria before the water reaches a filter. Skipping the retention tank is why some injection systems still stain and smell: the chemistry had no time to finish. Our chlorine injection system guide covers sizing that contact time for the water you have.
Maintenance and the signs of trouble
The single most useful habit is watching the level. A tank that is not going down means the pump has lost prime, the foot valve strainer is blocked, or the injection check valve failed and line pressure is holding the dose back. A tank going down faster than usual points to a leaking suction line or a pump running when it should not. Clean the tank when you change batches rather than topping up onto old sludge, particularly with soda ash, which settles and cakes. Verify the result downstream with a residual test rather than trusting the pump's dial.
Questions people ask about chemical injection tank
How big should my solution tank be?
Big enough that a batch lasts several weeks at your household's water use and dose rate. Larger tanks also allow a more dilute solution, which is gentler on the pump and safer to mix, so err toward the larger size if you have the floor space.
Can I pour undiluted bleach into the tank?
It is poor practice. Concentrated solutions gas off and can vapor lock a diaphragm pump, they degrade faster, and they force the pump to meter tiny volumes precisely. Diluting to a working strength gives steadier dosing and easier handling.
Do I need a retention tank as well as the solution tank?
Almost always. Oxidants need contact time to react with iron, sulfur or bacteria before filtration removes the result. Without retention, the chemical is still working when it reaches your taps, which shows up as smell, taste and stains that never quite clear.
How do I know the injection is actually working?
Test downstream rather than watching the pump. A chlorine feed should leave a measurable residual before the filter, which inexpensive test strips will show. Combine that with a falling solution level over a normal week of water use and you have proof the system is dosing.