I set up the 10 gallon approximately the 1st of August and it is still holding a slope 2 months later. STS seems to be a little heavier than Soilmaster Select or Turface and it has multiple grain sizes from small to larger and I think those aspects help it to maintain a slope.
75 Gallon, 2X55W AH Supply CF 8800K, 1XMarineland Doublebright, 2X Marineland 350 Magnum; 45 Gallon Tall, 96Watt AH Supply CF 6700K; 30 Gallon Long; Fluval F&P 2.0 36"/46W; 20 Gallon, 1X26W AH Supply LED kit; all with Press. CO2; (Calcined) Montmorillonite Clay
Greater Seattle Aquarium Society (GSAS)