I don't think you need water to use it. You could install it and blow a fan over it.
You can try using two on something small like a 20 gallon aquarium. I honestly don't think you're going to get a temperature drop that justifies spending that much money. If you cover your terrarium sides with insulating foam, that will help to keep it cooler using this. If you're like me, you like prefabricated products and don't like DIY. Unfortunately, there are no prefabbed terrarium peltier coolers that I'm aware of. If you don't mind DIY, you can get peltier units on ebay. Getting many will cost you less and you'll get better results. Still, you'll need to really insulate your tank, and it would only be practical on a small tank.
If you still want that, the return policy is 30 days for an UNOPENED product. If you can find a place that sells them and accepts a return of an opened but otherwise perfect product, even if it's more expensive, try them. The reason it won't matter if it's more expensive or not is you can decide if you like it or not (don't think you'll get enough of a drop to justify the price, honestly), then return it for a refund and if you decide you like it, get the same thing at the place that sells it for $40 less. You can likely install it without affecting the actual unit (like the stuff they use to install bulkheads) to test it out on a terrarium (since it won't be touching water) to decide if you want to return it or not.
You'll have to cut a hold in your glass. To test it out, build a replica of your terrarium out of cheap acrylic you can get at home depot. That way you won't have a hole in your glass for if you decide you don't like it, and you can use the other four/five acrylic sheets that aren't cut (or re-cut the one you cut) for something else. New terrarium, or covering an existing one are good idea.
I mean.. you can use that POS designed for nano tanks to lower the temperature five degrees (whoop-di-do, five whole degrees!) or if you're positive you want to cool thermoelectrically you can buy these bad boys.
http://cgi.ebay.com/FOUR-Giant-Ther...ryZ42910QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
That's an amazing deal, and if you're prepared to spend that money I'd jump on it. He'll likely not accept a return (you could always ask, worst he can say is no), but you can always re-sell them or trade them for plants!
If you have a larger terrarium, then AC or using a refrigerator is more practical. Use a portable AC unit that utilizes a small hose duct, and before the cooled air enters the terrarium splice another tube connected to a humidifier that's connected to the same timer/thermostat the AC unit it connected to onto the AC unit's tube. I'd imagine closer to the AC unit, the better it would be since it would have more time humidify the air before it reached the plants would be better, but that's theoretically. Practically it shouldn't matter as long as both come on at the same time. Taking apart a refrigerator and bending the tubes to suit your space is an option, but I'd probably screw up. You could remove the tubes and put in new ones and fill with new coolant, but I'd probably screw that up, too
You can cut a hole on both sides of a small mini-fridge or freezer, connect a small duct coming from your tank on one side and going back up into your tank on the other side,seal it with silicone, and add a fan to blow warm air into the freezer/fridg which would be cooled then head back up into the terrarium on the other side. Set it on a timer and use a two thermostats (in case one malfunctions, you'll be glad you used two) and you're good to go. One dude did this for a large orchidarium and it worked well. OR, I wonder if using one tube and using a fridge that's been modified to hold water (or a small chest freezer) and adding an ultrasonic humidifer to pump the tank with water vapor at your desired temperature until the tank is where you want it to be, then a thermostat would would cut it off. I imagine this would eliminate the need to water your plants if you did this nightly.
OR get a chest freezer, take off the top and replace with glass or acrylic, hook up two thermostats, add a fan or two for air circulation and use that as a terrarium. Not aesthetically pleasing but functional and will work well. I was going to do this, had the parts lined up, knew just what I was going to do until I read a stipulation about electrical outlets and the number of cords you can use in my college rule book, and I didn't feel comfortable skimping out on anything for the sake of not using too many cords so I decided to forgo that until I have my own place. Hopefully in four years. At least I know just what to do and won't have to research and investigate it again.
ANOTHER more complicated and expensive option is to get a REAL aquarium chiller, have a water basin in the bottom (keep it clean, don't let plant water contaminate it), run it through the chiller and cool it to your desired temp. Add a fan to homogenize the temperate (you should have one or more fans regardless!). You could also have a separate pump to pump it through a tube fastened to the wall/walls in a ununununun pattern. This would be like a radiator. Use a fan to blow air over it. REAL chillers are expensive an this isn't as practical as the above options. Just saying you can do it if you wanted.
Regardless of how you cool, insulating the sides, bottom, and back (and front if you don't care about not seeing through the front) will make your cooling more efficient. You can cover the sides you don't mine not being able to see through with Mylar before adding insulation to increase your light. It really, really makes a big visible (and invisible
) difference and this should be done whether you insulate or not to get the most our of your light. I think acrylic has better insulating capacity than class, so using an acrylic aquarium and / or acrylic covers would make it more efficient.
I hope this helps. Cooling is very doable and successful with some ingenuity.
