Why would you want this? For automated water changes.

I used to change about 2 gallons each day. It was all automated. With it, my tank would thrive since I was replacing trace minerals. It gave my tank a lot of room for error.

To use it, you have the two pumps. One set to pump in, the other would pump out. Since they pump the same amount of water in a time period, you would never have to worry about salinity changing.

I credit this as making my tank bullet proof.