Are you talking turnover rate thru the sump? If so, this would scare many people away. You probably mean 20 to 40 times turnover total water movement. Just wanted to clarify that so he doesn't go out and get a massive energy hogging pump he doesn't need.
The main thing has already been said...stability. A reef tank will run better at poor parameters that are constant and steady better than one who has perfect, then not so perfect, then perfect, then not so perfect.
Salinity changes are by far the easiest of all the parameters to keep constant. So figure that out and your probably going to be good to go.
Keep your water changes spaced out evenly. Don't do one this week, 2 next week, then wait a month and do a big change because its been a while. Keep it scheduled. Not saying that's what you doing, but just a thought to keep in mind for the future.
Try taking your filter sock off if you remove your sump sand. Unless you change that out every other other day, it's not helping. Even then some will say not to use one.
Do you have a regular thermometer? If that sticker one is old, it could be off.
Take that sand out of your sump. Doesn't look clean. Trapping all kinds of junk down there. That will only help you situation. Use that space as a settling chamber to get rid of detritus. That sounded kind of mean...sorry. not trying to be. Just trying to help so you don't get frustrated and give up.
