i could not find a krylon fusion clear spray paint in any of my local stores... i did find just Krylon clear acrylic... is this aquarium safe once cured?
Marble is composed mostly of the calcite form of limestone. It won't have nearly the effect on ph and hardness as other forms of limestone such as aragonite or dolomite. Unless you're keeping blackwater fish or others that truly require soft water it won't be a problem.