I have a betta in my 10g and many have said that 8.2(that's what the water is in the tank) is too high for them but he seems fine with it. I think as long as it's stable, that's the most important thing. Also, I have heard of others saying that their pH has dropped in their tanks after awhile but I have yet to see that in mine and it's been set up since July of last year. The pH in your tank just might stay at 8.4.
You could try using bogwood or peat but with the oyster shells in your soil, it probably won't even work but I could be wrong.
As for the filter, is it new? My AquaClear 20 was rather loud for about a month until crud started to build up in the impeller well. Now I can't even hear it anymore. I also have a
baffle on the outflow of the filter. It helps to lessen the surface agitation a great deal but if you really want to remove the filter, I can't see why you couldn't remove it from your tank. I know a lot of people don't bother with filters or powerheads in their NPT's. For the longest time, I didn't have any water circulation in my 10g and once I had added the filter, I had noticed no difference with the algae that was in the tank so I don't think it would get worse if you removed the filter.
