Evaporation help!


Reefing newb
My girlfriend recently bought a 5 gallon freshwater tank for her work, we set it up and followed all the directions, but we can't get the water level to stay as it keeps evaporating and we have to keep putting water in it(which changes the ph as we are using tap water).

Any suggestions? I looking into other types of water, but get mixed views depending on the website.
Rule of thumb is check the pH several hours after adding so it has time to mix into a homogeneous mixture. Evap is a part of life, but if yall want a better water, RO/DI is really the only way to go. Eventually at some point, tap water WILL cause problems from too many minerals. As long as your pH stays fairly steady, I wouldn't worry too much as it will fluxuate naturally anyways.