how much water does a 30 gallon evaporates daily?

[reefy]

Thanks guys. I do have diy led as well. Water doesn't evaporate much. Because I have a dosser that has 4 pumps(cal,all,mag) and I have one unused. So I just thought of using the extra pump just for topping off (RO with "Foz down") foz down is a phosphate remover solution which I am planning to add it to my top off water. Because I have a sumpless biocube and is isn't enough clearance to run gfo... As for now I am topping 50mls/day of RO which seems like it needs more