Why would you eventually have to add water a tank full of fish snails and plants?

You would eventually have to add water to a tank full of fish, snails, and plants for the following reasons:

* Evaporation: Water naturally evaporates from the surface of the tank, especially in warm or dry environments. This loss of water needs to be replenished to maintain the proper water level.

* Plant growth: Plants absorb water to grow and thrive. As they grow, they use up the water in the tank, requiring you to add more.

* Fish waste: Fish excrete waste, which can contaminate the water and increase its salt content. Replacing some of the water with fresh water helps to dilute the waste and maintain water quality.

* Snail activity: Snails also contribute to the water's evaporation rate and, depending on the type, may produce waste that needs to be diluted.

* Top-off water changes: Even if you are not doing full water changes, topping off the water level periodically is essential to prevent the water level from dropping too low, which can stress your fish and plants.

Important note: Always use dechlorinated water that has been allowed to sit out for 24 hours to allow the chlorine to dissipate.