Thank you for all that info. I would surmise something caused a mini-cycle as we term it, or of course the initial cycle was peaking. Cycling a new tank takes anywhere from 2 to 8 weeks normally; it varies depending upon many things so one can't be precise. Whatever, I believe the "washed-out" appearance is indicative of stress from ammonia and/or nitrite, both of which are highly toxic at any level you can test with one of our basic test kits [you don't say the number, when providing info always give numbers so we know more exactly how significant/serious this or that may be]. "Toxic" meaning the substance is causing stress, which can be little or great. Unfortunately, ammonia/nitrite "poisoning" can cause internal problems that may only surface weeks or months later with increased health issues or early death.
The pH would concern me if it is that high. Neons and cherry barbs prefer soft, acidic water, and while tank-raised fish are accustomed to harder basic water, there is bound to be a limit. I am not suggesting this was/is the issue, but at the same time it would add some degree of stress if the fish are having to internally counter very hard water.
I would not add any more fish until it is certain things are "normal," and that means a couple of weeks. Check ammonia and nitrite periodically, maybe every day for a few days then less often, say before the water change. [I trust you are doing a partial water change every week, without fail? This is very important. You can change 1/3 to 1/2 the water using a good water conditioner every week.] What is the nitrate test number? While less toxic at lower amounts, nitrate is still a concern if it is high or rising, as this indicates something is off biologically and this can trigger other things too.
Live plants will certainly help. Are you using any fertilizer?