Nature 2 and ozone are not enough by themselves. You'll get verying opinions, but I shock once a week with clorine and use 2 tblthingys of MPS three times a week or after every soak if that's more frequent. I have ozone and Nature 2 in a 400 gallon tub. I've been doing this since March and it has worked for me. My water stays clear and test good. I always leave the cover open for 15 t 30 minutes after I shock with clorine because I've seen it suggested on this forum to keep from harming the stiching in your cover or something like that. Happy tubbin'!