Hi Leslie, very nice tank. I agree with above comments on sand bed. I have just rejoined the reefing hobby, hence my later response to your thread.
I wanted to comment on the cyano you had. In general it will grow in response to excess nutrients which your higher nitrates are showing. Having good water flow (and getting rid of the crushed coral) to keep dead flow areas from forming helps quite a bit and doing routine regular water changes to dilute the bad stuff. If you are overfeeding the tank, this can creat excess nutrients, but I am a fan of keeping the nutrient levels high for the inverts/sand critters and corals, and doing water changes to keep the water health. Consider getting some critters to populate your sand bed to help eat the detritus - the two best i know of are GARF (their grunge) and IndoPacific Sea Farms. Then you should not have to siphon the sand, the critters can keep it clean. By keeping the same routine, this will help the tank adjust.
regarding your tang. any chance of catching him and taking some pics quick? sounds like maybe gettin picked on but concerned if fins are eaten away and white growth.