Water changes

[Aquattro]

Personally, I think as long as the water is the same temp and salinity, change as much as you want as long as it's the same bucket of salt. If it's a new bucket, I'd test a few more things, pH and Alk specifically. I would of course suggest that there is some degree of confidence that the water is the issue. I've done up to 90% changes before with no problems other than using most of a bucket of salt. Make sure it's pre-mixed for a day though, or heavily mixed and aerated if required same day.