hopefully other people with more experience can chime in. But if you use the aquarium safe silicone, I don't see why not. The only issue is with drying time, in an established tank, what will you do with the fish and decorations? I think the cure time is over 24hrs. Also, some stone will have an effect on the PH over time. Is it painted now? You could consider putting it on the outside (backwards) to let it show through! Then you have nothing to worry about! (maybe excess weight is another consideration?) Good luck!