In this instructable, I will be showing you how to make a 3D interactive background that has caves, and a underwater sand fall. It's quite easy to make, and is very cheap. It takes time, But the end product looks amazing and your family and friends will be left in amazement. Another great thing about this project is the price. The background only costs about $30-45. Depending on where you get the stuff. This is my second aquarium so I wanted to do something different then the average tank. The good thing about these backgrounds are, they are each unique, and they are cheaper then a medium sized ornament at the LFS.(local fish store)

Step 1: Getting the Equipment

The first thing you obviously need is the equipment. For this project I bought a 45g tank but you can make a background for any size aquarium you wish. I bought 2 boards of 1/2 inch closed cell foam at my LHS (local hardware store). It was purple and had a panther on it. I think it was 10ft long each board and I paid about $7 each for those. If you want to make this project cheaper, I heard you could use open cell foam that you can get for free at the local furniture stores. Next you'll need silicone. I provided a picture of the stuff I used. It was about $8. To cut it you can use a razor. I used a hot knife and would highly recommend you do the same. It made it soooo much easier and did much nicer and cleaner cuts. Lastly, you need the cement. I used a hydraulic water stop cement. It's a powder that you add water to in order to make it thicker or thinner. I used the whole bucket. It costs about $15 (the most expensive).

What you need

-2 10 ft foam (I used 1/2 inch)

-silicon (make sure it's not mild/mildew resistant. I used all purpose clear silicone 1) do your research on the silicone

-a knife, preferably a hot knife

-hydraulic water stop cement

Step 2: The Design

I started by measuring the size that I wanted the background to be. Length, height, and width. Since my aquarium was 4ft long. I left room on either side of the background in order to put plants and stuff there. If you want, you could put it the full length. I used symbols not the pieces I cut so that I know where each piece of foam laid in the background. You can use your own method of this. I suggest that you include the layer, and side. As I cut it, I made up the design layer by layer as I went. I knew I wanted lots of caves and a spot for the sand fall. So I made a little pooling area for the sand on the right where I would drill the holes later on. On this layer, DRY FIT ONLY. Just in case you don't like the look of something. Imagine that the back glass of your aquarium is behind the structure. So make the back as flat as possible.

Step 3: Silicone It!

Now that you have the design, you can stick it all together. BEFORE I tore the dry fit struck apart, I made marking on where each piece was in relevance to the next. Just so it's easier to put together. To silicone it, I put a garbage bag laid flat one the ground so I would make a mess. I put a board flat behind it because then you are for sure getting a flat back on the glass. Depending if you have a cross brace across your tank, you might want to separate it into two parts so that it could in inside the aquariums nicely. I made that mistake too late and had to backtrack. When silicone gel the pieces together, do it in small groups. Put weights on top of them so that they stick nicely. I used cans and food item.... I got hungry.

Step 4: The Sand Fall (Optional)

Your can skip this step if you don't want to involve this in your background. It will cost a bit of extra money. About $10 if you have air pumps, if not, about $20. You need the height of your background of 1" PVC pipe. And a 90 degree elbow. You are going to cut it to the height you want front the bottom of your background. Then attack the 90 degree elbow to the top of the pipe. Also at the bottom, cut an angle about an inch up to halfway back on the pipe. Next your going to drill two holes at the top of your elbow so that the air hoses fit through the snug. This will be staying dry fitted. As you could see in the picture, I filed the foam down to make the pipe fit nicer. I drill a hole from the back to the front right over the sand pool area. I left a hole leading back up. So the air would rise out of the back, but the sand wouldn't. If you do this correctly, you need a light sand. I used silica sand from pet smart. Basically trail and error but I got it first time.there are pictures to help with this. There are some pictures in next step to get the picture too. At the bottom of the sand fall, you can put a screen so fish don't go into the pipe, but I didn't bother. You will also want to put a slant downwards so that the sand could roll into the pipe easier creating a better flow. There is a picture of the sand fall with a smaller pump at the last step.

Step 5: Support the Structure

With the extra foam board, cut out the same design as the back of the structure by tracing it. This is just to make it flat against the glass and for it to stay better. This will not only make the structure more sound, but also will add a bit more depth. You need to do this twice. Ignore the PVC pipe if you are not doing the previous step. For those that are, the last layer, don't go all the way through the the board where the PVC is because than its hidden better and you have more area to work with. Lay it down with the the PVC pipe between and after its silicone to dry. Weights again to bond it better.

Step 6: Cementing

Now time for the cementing. If you want, you can put colour into it to make it look more rocky, but I found that this looks pretty good just the way it dried. I made it rough to make it more rocky. But ya, you are going to start with a thin coat of the cement in order to give the other thicker coats something to stick to strong. You will be putting about 3-4 coats in. Don't put cement on the bottom or on the back. I did a light coat and it fell off. So just leave it. And try to keep the back flat for a better stick. Leave it for about a day to dry in between coats for a full dry. If you split the structure, don't cement where you will be attacking the two together.

Step 7: The Placement

Now it's time to put in the background!i put paper down at the bottom of the tank so I wouldn't spill cement on it. If you had to split the structure into two parts, you want to put in in the aquarium separate then silicone the pieces together and do a coat of cement to hide the bond.then you will wait until that dries. I showed a picture of the bond I did. Now that the structure is in the tank, your will have to raise it a bit due to the silicone on the edges of the glass making it not flat. So just put down foam pieces to raise it above the silicone. Now your are going to glob the silicone on the back. You might need another bottle of silicone. But don't be scared to put to much, you really don't want it to loose it's seal to the glass and pop off. It's very annoying. Again, another mistake I did. But ya. The supports I talked about will be shown in the pictures. You will leave the silicone a day or more to dry because it is such a great amount. In the picture, I didn't put enough silicone.... PUT MORE.

Step 8: Decorations and Filling

Now fill your tank, you can put the decor in before or after the water. I personally like doing it after I fill it. The water will be very cloudy and the PH will literally sky rocket. It will be off the charts. So don't put anything live in it like plants or fish. It will take a few weeks to get the PH back to normal but it will get there. Be careful about checking the PH because it could still leach off of the cement. Better to be sure so take your time. I recommend doing a water change every 1-3 days. I decorated my aquarium with driftwood and plant and silica sand. Also with black rocks I found in a stream near my house. I boiled them to get the bacteria off. You can test the sand fall and move sand around to where it works.

Step 9: Now, for the Finishing Touches

After the PH is stable, you can add plants and fish. I put my plants in 1-2 weeks before the fish so that they can establish their roots. I will soon be putting cichlids in here. But ya. Now you can say, I made that and it will look very nice and look astonishing. For my 45g, I have two lights one main LED that I made and one plant and aquarium fluorescent light that I bought for $35 at Home Depot. Also two filters and two heaters. But I am very happy with this. If you are wondering how much I spent creating this aquarium with the stand and everything, I spent about $300. The dresser I bought at a auction for $47.50 and it's pure walnut. Let me know what you think and if you have any questions you can write them in the comments. I WILL ANSWER THEM ALL! And be sure to favourite this thanks.