Tank is looking very nce!
I see that you had a reboot due to sand bed issues. Sand beds are one of my favorite topics, so I thought I'd share some info/techniques that should be helpful in maintaining a thriving tank for the long term.
IMO, at least occasional vacuuming of an accessible shallow sand bed is very important to a system's health. But, there is another part of this process that is often overlooked which I find especially important for nano reef aquariums due to the usually high ratio of livestock to water volume.
Whether medium or fine grain, advective forces will push the detritus down into any sand bed. Basically, the more flow the further down the detritus will decend. Same is true if there is an obstruction in the way of the flow, such as live rock (see 'Reef Aquarium' Vol. 3, pgs. 263-264 - Sprung/Delbeek for detailed analysis). Because of this phenomenon, I vacuum under one base rock area every 3-4 months and then move on in a few months to a different base rock, etc. This way I avoid disturbing too much all at once, which could potentially destabilize a tank (especially if this process hasn't been done before). The amount of concentrated detritus removed from these locations is staggering! This is for shallow sand beds only as deep sand beds are a whole different proposition
It's a bit of extra work, but more than any other process I credit this 'under the base rock' cleaning technique to the health and longevity of my 6+ year old Nano.