It occured to me that I did not respond to question regarding sand for the Oscar tank. Personally I love sand substrtate for most fishes. But some of the larger cichlids enjoy rooting around in substrtate and for this reason, I wouldn't use sand for Cichlids such as Oscar.
I not to long ago rinsed ,and rinsed, and rinsed, approx, 90 lbs of sand for eighty gal tank housing one electric blue jack dempsey,one synodontis multipunctatus,and one white spot pleco. It was a mistake. The jack dempsey and synodontis were quite proficent at stirring up the sand to the point that I feared it would ultimately wind up in the impeller assembly of the filter. Sand is also favored by many because the waste remains on the surface of the sand and does not become lodged in the substrate like it can do with gravel thus making vaccuming the bottom during water changes easier. Problem was,, my fish were digging around or rootiing around to the point that the waste was being buried in the sand rather than lying on top as it normally would with smaller fish or non diggers.
Long story short,, I would opt for natural colored river gravel or pea gravel which can be found at many garden or landscaping stores for much cheaper than the bagged stuff sold at fish stores or online. I paid 12 dollars for 75 lbs of this gravel to replace the sand removed from the eighty gal I spoke of. It will require rinsing to remove all dirt and dust but it looks nice and as mentioned,,tons cheaper. I would recommend not making substrate more than two inches deep maximum. I have an inch and maybe one half in the eighty gal and it makes gravel vaccuming much more efficent than it would be with deeper bed. Hope some of this helps.