you can also spot feed certain corals using the method in this thread
https://forums.saltwaterfish.com/t/268119/how-to-spot-feed
the corals you listed don't really require spot feeding but you can add coralfod to the tank and they may benefit. the xenia is almost a pure photosynthetic so it...
I have always fed the "juice" to my tanks and always will especially when they are full or near full of corals. all those littel meaty bits are great foods for the filter feeders, benthic organisms and microfauna of the tank as well as being (dependant on the size of the particle) appropriatly...
its definitely not doing well, browning out and lack of polyp extension are bad signs. tough to say whether it needs more light or flow but I would bet on lighting try moving it to a brighter location with good intermittent flow.
I think you would be fine with a skim coat of sand in the bottom for looks. you could also silicone the sand down for the bare bottom effect with the sand look.
I wouldnt bother upgrading the return pump. the stock pump should be just fine.
looks like a normal diatoms to me its not even a bad case of it I have had far worse no worries. stir the top layer of the sand to force it to cycle its life faster. the diatoms will bloom and consume silicates by buryting them you kill them and force new diatoms to bloom consuming more...
getting frusterated with doing everything left handed, thanks for the words of encouragement guys. 3 more days officially according to the docs before the stitches come out.... I just pulled them the cut is sealed I need the little holes to seal up too so I can reach in my tank again.
I dont think its very high quality live rock. it may be bacterially alive but there is little else on it. Some light coraline here and there but overall its very poor excuse for live rock. IMO