Permanent Pebble Substrate


This is another idea, similar to the permanent sand substrate. Please note: I do NOT actually recommend repeating this project! At the bottom of the page, I will explain the drawbacks, and suggest some alternatives.


This is the product I used. It is basically "Great Stuff" expanding foam, but in a black color.
I spread it on the bottom of the tank. The foam comes out very slowly, so this is very tedious.
Then flattened it out. This is where I realized that the foam was not behaving the way I had expected. I didn't realize that it would completely "deflate" as soon as I touched it with a spreading tool. I had to apply quite a lot more foam to get enough material down for the pebbles to stick to.
Then sprinkled it with aquarium gravel. During drying, some of the thicker areas of foam-goo re-expanded. After the first attempt hardened, I added an additional layer of foam and pebbles around the side edges and back edge of the tank. Overall, the project used a LOT more pebbles than I had expected; be sure you start with plenty of pebble material.
This is the finished product, in use. One problem is that the bits of pebbles and foam leave plenty of places where blackworms can escape and hide. This was something I had been hoping to avoid.
Finished product.
Finished product, showing how well the blackworms escape into the crevices.
The animals seem happy enough with it. The tank was made for juvenile Japanese firebellies (Cynops pyrrhogaster).

There are a couple of problems with this tank. It leaves too many crevices for blackworms to hide. The expanding foam did not behave the way I expected. It continues to expand, even after being flattened, and after the pebbles are placed on top of it. It is impossible to manipulate the material (to move or shape it), because as soon as you touch it, it completely deflates into a small amount of sticky substance. When the material dries, it isn't black, but a silver-gray color.

If I were going to repeat this project, I would use black aquarium silicone instead of the expanding foam. It is much more "predictable" in its behavior, and much easier to work with, in my opinion. I also would opt for a smaller size of pebbles.

2007 Jennifer Macke