You can, for small changes on a small tank. You want to make sure that the 2 Chanel’s are dosing the same as each other. Even then I would keep an eye on your salinity. Most dosing pumps are designed for very small volumes. Dosing pumps fail over time as the hose becomes elongated and no longer function as original. This will happen faster the more you use them. Also the rollers wear and the motors fail. For these reasons they do not work well for larger tanks.