I think it would work if you add a lot of leaves on top of it. Not sure if miracle grow has clay in it, which you would want, and does it have enough sand? I had the idea you could put a fine net over the leaves, weighed down in the corners, if the worry is that you couldn't find a dead fish that floats deep into the leaves. I think it would only work though with rainwater, as city water has chemicals used to reduce cloudiness, the city water in my tank turns to bacteria much faster than rainwater, almost immediately. I would have a bubbler, and a wavemaker with dimmer switch to not kill the plants, the wavemaker used occasionally. A deeper tank you could have if you use a filter that has a long tube that goes all the way down to the bottom to circulate the water.