0.68 is higher than most people like to keep their tanks but there are a lot of highly successful reefers that have higher levels than that. Every tank is different so it is hard to say 'lower this' or 'raise that'. Your tank is a unique ecosystem. What matters is how the livestock look and behave and how your rock/substrate is handling the bioload. If you sand is clean, you're not getting algae or bacterial outbreaks, and your livestock looks healthy, I wouldn't mess with it other than maybe make sure you aren't overfeeding.