Interesting. My oscar would always sift through the gravel so it was never an issue. It's amazing how many pebbles they can fit in their mouths lol,
But I have had this experience with sand. I bred salvinis in a 55g with play sand and with all of the fry food I was adding the water started to smell a bit and get cloudy, which I have only seen in heavily overfed (or uncycled) gravel tanks. But i guess if you siphon the detritus from the top of the sand and stir it daily you won't hit those issues either. I ended up switching to gravel and my problems were over. I even grew the fry in the tank for a couple more months after that. I just siphoned all of the sand out, black patches and all.
However, simply adding other things for the bacteria to colonize on would be fine too such as another filter or even just some biomedia in the tank itself. I have some old filter wool sitting in a QT tank of mine in case I need to move some bacteria somewhere. It's currently helping to handle the feed load from my electric blue acara fry.
