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Replenishing the SNAP Working Solution

Learn how to properly replenish the working solution of SNAP grow boxes.

Replenishment of the SNAP working solution inside the grow box is an important part of maintaining the SNAP Hydroponics system. The amount of working solution inside the grow box will decrease over time as the solution gets depleted through evaporation and transpiration. In addition, the concentration of nutrients in the solution will decrease as the plants consume them to power their growth.

When initially set up, the bottom of the seedling plugs are immersed in the working solution by about 1–2cm. The working solution enters the cup through the slits and saturates the growing medium. Because of this, the seedlings grow in water logged condition.

Initially, the bottom of the seedling plugs is immersed in the working solution by about 1–2 cm.

To survive being water logged, the plants grow aerial roots. These are roots that are not totally submerged in water and are exposed to the moist air within the grow box.

Aerial roots has grown and the working solution level has gone down.

As the plant grows, more roots will develop and make their way into the working solution. Evaporation and transpiration will reduce the working solution level until it is no longer in contact with the bottom of the cups. At this point, if everything is going well, the medium is no longer in contact with the working solution but the plants still have access to the working solution because roots have grown out of the cup through the slits and into the working solution. The rate at which the working solution level decreases will increase as the plants grow larger.


It’s important for the roots to immediately grow out of the seedling plug and into the working solution so it won’t get “left behind.” That’s why it’s important to have just a little amount of growing medium inside the seedling plug. If there’s too much, the roots will just wander inside the seedling plug and will not grow out towards the working solution.

More roots have developed and the plants have grown significantly.

As the plants develop further, more of the solution will be consumed.


It is important to regularly check the working solution level and never let it dry up.

The working solution level is low and needs replenishment.

To replenish the working solution, add fresh working solution or plain water (details below) to increase the working solution level so that it is just below the bottoms of the seedling plugs.


DO NOT return the working solution level to its initial level because this will very likely submerge a majority of the aerial roots and cause the plants to wilt and stunt their growth or worse, kill them.

Working solution level replenished and is sitting just below the bottoms of the seedling plugs.

Leafy vegetables generally reaches marketable size by around three to four weeks after transplant and normally doesn’t require replenishment. In cases that they must be kept beyond a month, or if the working solution level has gone down faster than normal (specially in the summer months) and the working solution level must be replenished, they should be replenished with plain water. This is because the working solution still has enough nutrients to fuel the plant’s growth until harvest.

For vegetables that require a longer growing period, replenishment with fresh working solution is required every month. In most cases, the working solution level will go down sooner than a month especially for large plants that transpire water faster. In this case, replenish the working solution level with plain water.