So a co-worker gave me one of those "roman column" looking tank ornaments. It's pretty much hollow inside. I like the look well enough, so I was thinking of filling the inside with sand and siliconing the bottom. Anyone done that sort of thing? Do you think it will hold?

I suppose I could just plug the bottom with silicone without filling it up, but I also wanted to make it a bit heavier since it's sort of flimsy-feeling right now.

Other memebers have done similar things for sure. I've got two hollow ornaments as well, I'm thinking of drilling holes in the top and putting airstones in them.

A few well placed holes make for a lovely effect in the tank. I just returned my hollow ornament to the store and bought a smaller one. Gave my fishie more room to swim around in.

Making holes for airstones also sounds like a great use for hollow ornaments... but then it must take some creativity to hide the tubing? I suppose some judicious camouflage with silk plants...

I have a hollow ornament, too, and I'm thinking of filling it so it's not hollow. What exactly should I get? Is there a special aquarium sealant that I would need? If it's a small ornament, can I just use the sealant and not the sand?

I have a hollow driftwood replica ornament that I put an airstone in. The ornament alrealy has a few holes on top and back. The air line leading to the airstone comes down the back of the tank and is held in place by a couple of suction cup airline clips. the ornament is in the middle of the tank, so the portion that leads from the back of the tank to the ornament is under the gravel. I adjusted the air output so that the bubbles do not come out in a steady stream. Rather, the bubbles come in short bursts - I find that very pretty.

Aquairum sealant tends to be thick, gooey stuff. It does not fill in very easily or well. You cannot just pour it into an ornament and expect it to flow in to fill the nooks and crannies. This is why sand is regularly recommended.

If you seal an ornament without sand or some weight inside, the trapped air will cause the ornament to float - even heavy things will still float in many cases.

My favorite method of filling an ornament is to seal any small holes in the ornament with sealant. When this is cured, I then pour sand in from the bottom to fill the hollow spaces. I then melt food grade wax and pour it into the ornament. The wax will flow in and through the sand, sealing it into place and filling in any hollows. When the wax cools, I then seal over the open end of the ornament with aquarium sealant.

If you look at online pet stores and fishkeeping supply stores, they sell silicone that's actually labeled "aquarium sealant," and it's not particularly expensive (like 5 bucks for 90ml). You can also use some kinds of silicone that they sell for regular construction purposes but you have to be careful which ones, like anything with anti-mildew ingredients is a bad idea. I'm sorry I can't remember more specifics about those.

If it's small, I am sure just plugging the hole would be enough. I was mainly concerned about the weight of sand in mine.

Ok, got the sealant, but since it's not canning season, I can't find food-grade wax. Can I use a plain white, unscented candle for the wax?

Yup. Seal it over with the aquarium sealant when done such that no water is in contact and there are no worries. (It is actually fine, without sealing, but I tend to be obsessive....)