I have a pet axolotl. They like water to be in the upper 60s F, and my ambient temperature is around the lower 70s. This isn't great on axolotls, so, they usually need something to cool down the water. Thing about axolotls and a few other water pets is that they require special attention. I've learned that to cool off the aquarium requires either lots of money or lots of invested time.
There are a few options out there...
Buying an aquarium cooler- Effective, though expensive, at several hundreds of dollars
Making an aquarium cooler out of a minifridge- At maybe a hundred dollars, much more affordable, but requires a lot of expertise in electronics that I don't have, plus it's unsightly
Crank the air conditioner really low- Great for the axolotl, though uncomfortable for the humans (and expensive)
Put ice cubes in the tank every few hours- Works, though you have to be pretty committed to being regular with it
Personally, I bought a new house recently and one of the air conditioning vents is missing a cover. I haven't bought a cover for it yet, but an idea hit me. What if I could channel that air conditioning to cool off the tank??
I had some leftover lumber from a previous project and built a custom fish tank stand that would self-regulate the temperature of the water. This stand is designed to sit directly on top of the air conditioning vent and funnel the cool air that I would already be using to go under the tank before entering the room. Cools off the tank, and my house.
Note: This is not an instructable on woodworking, rather a concept and an idea. I'm not going to go into any detail on how to saw/sand/screw the boards together, just the arrangement. I will be leave the details up to you and your preferences. Aquariums weigh a lot, so make sure you properly reinforce the stand as needed.
Step 1: Determine the Size and Fuction of Stand
I designed mine to fit between an outlet in the wall and a window, and to sit on top of a standard vent. Determine the size of your aquarium and how large you want the stand to be. There are many options on how to customize your stand such as cabinets for equipment and food, or to multipurpose the stand for other uses. I designed mine like a bookcase with some shelves underneath. Do you want doors to hide what's inside, or open to display? I decided to forgo the doors and use it as a display for some pictures and got some pullout bins for the minimal equipment I have.
Step 2: Build the Frame
First picture: This is the front of the stand. I started with the top, and screwing the sides from the top. This will provide a lot of good structural support later on, which the tank will need. Notice the rectangular hole cut in the top? That's where the air conditioning will be vented. This design will incorporate a funnel from the bottom of the stand and the air will flow out the top of the stand through this hole to cool the bottom of the tank.
Second picture: This picture is of the rear end of the stand, with the bottom attached. Note how the floor of the stand does not go all the way to the back, flush with the sides. This is where the the stand will sit directly on top of the AC vent.
Picture one: This is the back of the stand. The piece leaning against the stand is going to be installed in the middle of the stand. It's not the back of the stand, but it's the part that will be seen from the front, so make sure it's finished to your tastes. It also plays a large role of the structural support of the stand.
Picture two: With the center installed, this is the front of the stand that people will see. The storage capacity is limited because the back portion will act as the funnel for the AC vent.
Picture three: Here's a view from the top, going down through that hole. This is the unfinished vent.
Picture four: And here's what the back side looks like.
Picture five: This next piece of wood is going to be the backing of the stand, the final piece which will complete the the funnel. You can use whatever material you want, I just had this laying around, and as most who use Instructables think, you use what you have. This piece will not be seen, so it doesn't matter what it looks like. This piece will not be installed vertically, straight up and down. The bottom should be attached flush to the back of the stand, and the top should be attached flush to the rear side of the vent hole at the top, as shown in pictures six and seven.
Step 4: Establishing Airflow
Picture one: On the top side, along the side edges, attache some boards about an inch thick. This is what the tank will stand on, and the airflow from the AC vent will flow underneath the tank and outside the stand. The air will exit the front and the back. This is important so your vents aren't blocked. Your aquarium will be cooled, and your house will still get cooled as well.
At this point I added some shelves in front and stained the stand.
Picture two: I put four additional 2" x 2" blocks (two in front, two in back) to assist the weight distribution of the tank. I don't think they are necessary, but are a good precaution. Can't hurt. I didn't permanently attach these, they are just wedged in there.
Step 5: Using the Stand
This turned out to be a very sturdy and hardy stand. It can easily support my weight at 180 lbs, and made out of quality wood, should last a long time. As you walk in front of it, you can feel the cool air flowing freely out the front. When you want to change the temperature of the water, just set the thermostat. I like to keep a few ice cubes of tank water in the freezer as backup in case something goes wrong with the AC. I keep my thermostat set to 73-74 F and the water is always in the upper 60s. Of course there will be some fluctuation in temperature as the AC is not constantly running, but the temperature stays pretty consistent. It only lowers the overall temperature of the tank a few degrees, so it's not going to do any drastic changes, but it works for me, and I think it should work for most.