In two and a half weeks, I'm going to be setting up a 34-gallon corner tank. It will eventually house 2 dojo loaches, 3 peppered loaches, and a school of white cloud mountain minnows.
Right now, it has one golden dojo and 2 cories of uncertain species who came with the tank. It's a touch understocked.
With all these bottom-dwelling critters, I'm going to need an awful lot of bottom territory - the dojo and peppered loaches should share, but have not been introduced yet (peppers are in quarantine 2 weeks today!). So, how do I accomplish this without losing too much planting space, resorting to terra-cotta pots, or buying an ugly and overpriced commercial reptile product? I make caves. After a bunch of research, the most common method of cave-making (styrofoam and concrete) is not something I want to try; it's very very cold outside, I lack a garage, and I'm concerned about my ability to shape styrofoam into what I want. What I want is a cave with a profile like this:
where the bottom line is the substrate, the verticals are walls with cutouts for easy access by fish and easy viewing by humans, and the top has a tray. That way, I don't lose too much of the planting area, the caves look more natural once they're grown in (especially if I can coax a plant to drape down over the edges) and the weight of the extra dirt holds the caves down better... the peppers can be a little spazzy at times, and I could see them knocking furnishings around.
After a little research, it seems that polymer clay is safe for aquarium use after curing. I did several hours of internet searching for this, and came to the following conclusion:
1. The manufacturer of Sculpey states that polymer clay is non-toxic, but not food safe. I'm using this brand since I've used it before and like it, and it's available and fairly inexpensive here.
2. The final product is not food safe not because of any leaching problem, but because it's porous and might harbor bacteria. This is not a problem in the aquarium, where every surface harbors bacteria anyway, and where we typically encourage beneficial bacteria to grow.
3. Fired polymer clay is essentially fancy PVC and should have zero effect on water chemistry; it should not cause any more problems than a terra-cotta pot or one of those resin ornaments. Being PVC, it also should not decay and release anything nasty over the long term.
4. Many people, on many forums, have gotten scared off and have not tried this (or have not posted results). A very few have. Those few say it works. My source is mostly wetwebmedia.com, with a very few other, unrelated blogs.
With a little creativity, polymer clay can mimic natural stone in looks and texture. Unfortunately, I couldn't find any of the type that already mimics stone (it's called Granitex, and isn't available here. I will be going to a large city this weekend and may get lucky.)
I cooked up two caves over the last weekend. One mimics a plain grey river stone. The other was an attempt at mimicing black marble. They still look like fake rocks; at least they look like fake rocks that have half a chance of looking good if they're discreetly placed. Since these were tests, I did not include the substrate tray, and they're significantly smaller than the ones I want for the corner tank. First I want to see if the material works at all.
I fired them, let them sit for a full day, and then placed them both in about a pint of water, figuring that if they do not affect a small volume, they won't affect a large one. I'm well aware that they may leach something outside the range of my test kits, since I don't have fancy ones (API master kit, plus some cheapo 5-in-1 strips), but this is not the only test I'll be doing. Since my chemical testing ability is pretty pathetic, I'll be checking out how some of my pest Physa sp. pond snails like it; if they're fine, it'll get introduced to a small, established tank with fish.
The water parameters started at:
In three days, they have not budged at all. If that's still the case tonight, I will remove them from the little cup, place them in a larger bowl, and add some pond snails. Hopefully they won't die.
My favorite article on bio-assay
gives the (rather arbitrary) values of one day for acute poisoning, and a month for chronic poisoning. Since I have less time than a month to get this aquarium up and running, I will be shortening the bio-assay to about two weeks. I am fairly confident that this material is in fact not toxic; I just want to make sure of it before subjecting my favorite loaches to something unknown!
There will be no alteration of the pond snails' behavior (gasping at the surface, crawling out of the water, refusing to eat, or death) in one week of exposure to the caves. They will continue to eat, move around, and lay eggs.
The snails will be checked at least twice daily, twelve hours apart. I will record how many are live or dead, how many are on or in the caves, and how many are at the surface. If I get really excited, I may even bring them and their bowl to work for closer monitoring.
So... anyone done this? Thoughts? Glaring holes in my logic?