A bare bottom tank is very difficult to colonize. There is limited subtrate for bacteria films since there is no sand. The surface area from the grains in added sand is huge and there is none of that. The bacteria film will have to ramp up to meet the need if the environment is not too toxic. Add to that the toxins from rotting xenia and you do have troubles. Probably needs a skimmer, complete water change and/or carbon and a new bacteria culture. A sump with live sand and a refugium would help tons in this kind of tank. Its normal to have a normal 8.0 pH. Thats not something you can fix in salt water, its normal with the kinds of test kits available. Tyring to get a reading of more than 8 may mean you kill everything in the tank trying and still read 8.0. I recommend not trying to fix what isn't broke until you are an advanced chemist. Its likely to take Mg to raise that as well and there is no real point in raising it as its just not going to stay there. Each tank will balance at its own point depending on kalk, calcium reactors, dosing, etc. Just do good maint. and use the 8 as an indicator that means its good. If it drops drastically to less that 7.9 (the early morning pH) thats an indicator your chemical content is off and nitrates may be up from lack of water changes relative to your setup and consumption rates. Most tanks swing from 7.9 to 8.2 during the day. To get a pH of 8.2 to 8.4 you either have a late afternoon with lots of macro or lots of buffer and/or a high alk. Whoever wrote the book saying a pH has to be higher than 8.0 has a different test kit method and maybe different additives/situation. My newly mixed salt always has about an 8.0 pH with RO according to my kit and it works perfectly well without trying to change it.
Do what Richard said although once blood poisoning has set in, its fatal 99.9% of the time. I hate to say it, but, its probably too late already. Hope to be wrong on that this time.