Building a DIY Background
By: Jaster


Building a DIY Background

A couple weeks back a friend of mine decided he no longer wanted his fishtank. Being the good friend I am I told him I would be more then happy to take it off his hands. It’s something I’ve always wanted to do. So I ended up with a 80 gallon bowfront tank for my first tank. Gotta love it. All the tanks I’ve had before were just small 5 – 10 gallon goldfish killers so I wanted to do some reading and learning before I set this one up. Well let me tell you I was rather surprised at how much I needed to learn…

So now I have a general clue (thanks to the good people here at Badman’s) and I started thinking of what I really wanted to do and how to set it up. I knew I wanted something over the top that wasn’t just some sand and plastic plants. I very much like the old ruin look so I knew I wanted something like the Greek/Roman/Atlantis ruin type theme. I looked at every type of aquarium decorations you can think of and I didn’t like most of them.

Through all my digging and looking at other setups I found all kinds of these styrofoam backgrounds and knew this was it. My first thought was my god this is going to be hard as hell… I could never do something like that. I was shocked to find out how easy this was to actually do. If I can do this anyone can. The great thing is that there is no real wrong way to make this. It’s all up to you an what it looks like. The best part is how cheap most of the materials are compared to the cost of high end decorations.

One thing I did that I seriously do NOT suggest people do, is make this without your tank around like I did. Your tank will be your greatest asset to how things will fit and come together. What I did was very impatient and probably not the smartest thing to do. So now that everyone is asking “why did you then?”… I was lucky enough to have every dimension you could think of for the tank. I made my friend measure everything for me. Outside, inside, and right down to the slots in the hood for the filters. I have the filters here so I was able to measure where the down tubes will be and anything else either coming into or out of the tank.

I took a lot of time-making drawings and rough sketches complete with dimensions where everything in the tank will be and was sure to give myself a couple inches or ‘wiggle room’ in any given direction. So when I started making this, as much as the original background drawing changed through the project, I still knew where my boundaries were.

That was the only part of this project that remained constant. (and if my friend is off on his measurements I’m going to beat him to death with this background) Even though I may be a anal mechanical design engineer and I’m quite confidant my measurements will be fine, I strongly suggest you wait for the tank. Unless you are an overly impatient engineer that doesn’t mind taking chances like me…

So with that… lets build something!

Here is all the stuff I bought for this.

  • 3 3″ paintbrushes
  • 3 2″ paintbrushes
  • 2 boxes of quality toothpicks from the Dollar Store for $1-2 bucks each
  • 4 sheets of 12″ x 18″ x 1″ styrofoam from Michael’s for $35. you can get this stuff from just about any craft store
  • 4 pack of GE Silicone I from Lowes for $15.
  • 60 pound bag of ready to use Quikrete concrete mix, concrete coloring, concrete acrylic fortifier
  • A large can of Great Stuff expanding spray foam for about $30 from Home Depot

The other things you’ll need:
A good utility knife for cutting the styro, a caulking gun, a file or heavy grit sand paper and a propane or butane torch for shaping, a bucket for mixing the concrete, and a measuring cup. (hint here… don’t use a the kitchen ones unless you want your other half hunting you down. The coloring and fortifier will kill the cup… I used a big plastic cup from McDonalds and drew some lines on it at different measurements)

This is where it started… Like I said, I pretty much had a set plan of what I wanted and the space I had available to me… I just started putting things together. I started with 6×18 strip and put a 6×6 square at each end and a couple in the middle. I used the toothpicks, about 1 every inch or so, to hold it all together.

This gave me the first level and the caves. Then I used one of the full sized sheets and toothpicked that to the back of the box I just made for my backwall and just cut it at an angle I thought looked cool. Next I took another 6×18 piece and attached that to the front. This would soon become the front entrance of the caves.

From the scrap of the back piece I cut out some skinny strips for the pillars and a 4x8ish sized piece for the second level. I put the second level at a bit of an angle. I had seen this done a couple other projects and it works well for holding sand or gravel in place after if you wanted to do something like that. Personally I thought it also made it look more “ruin-like”.

Now I had what looked like a crooked bookshelf.


So this took care of one half of this and I repeated everything again to make the other half. Again using a ton of toothpicks I just joined them together. I was going to add another solid level but changed my mind and added more pillars to the very top instead. Once I had the whole thing together I added holes here and there along the front and through the inside walls for the fish to swim through.

All I did for that was poke a hole through the styro with my knife and started breaking away styro until I got what I wanted. Just keep in mind the fish you have or want and make sure the holes you make will be big enough for everyone to get through. Also keep in mind that you will be coating this in cement, so the holes you make will close up a little so make them a little bigger then what you think you need.

Onto shaping… All I really did here was round off the corners some with my fingers and the file. Broke off a few pieces here and there to add some randomness to shapes of things. Then I took my torch and very lightly hits a few spot to add dents in the walls and floors. (I suggest doing this outside or in your garage if you have one.

Melting styro stinks…)

Be careful here though. Styro melts fast and easy. However if you do melt through some place you didn’t plan you either leave it if you actually like, simply replace the piece, or fill it with concrete later.


Expanding spray is way too much fun. I actually had to get another can of this stuff because me and my 11 year old son being the children we are had too much fun writing our names on things and making foam mountains… He ever needs a volcano for science class I know what we’re using. So if you’re a kid too, get two cans…. I figured it gave me some experience on using the foam and how hard and fast to spray the stuff. That’s my story and I’m sticking too it… Through my playing… I mean experimenting, I found that a full pull on the nozzle will give a lot of foam very quickly. I suggest a gentler pull, just enough to get it come out will help keep the foam under control. Also even though you stop pulling the trigger the foam will continue to come out the nozzles. This drippage worked well though for making crumbled rocks and such around the background.

So when you start applying the foam, go around every seem and crack on the background. Inside and out… Don’t worry about applying too much here and there. Anything you don’t like you can cut off later. So once it was all sprayed and cured (let it cure overnight) I trimmed off what I didn’t want or like and took the torch to this one final time. This time with the torch though I lightly went over the entire background to melt it down some. When taking the heat to the styro it will melt and suck inward on you but it will also harden the styro some and make it a bit more rigid. The other slight bonus is that you can remove some of the buoyancy that this will have when you are done. The main benefit in my opinion though is the hardening of the styro.


Once this was all done I had decided that I really didn’t like the idea of siliconing this to the back of my tank. Reason being… it will leave a nasty mess on the glass if I decide someday to remove this. My thought then was to mount this to plexiglass I had hanging around and let it sit on the bottom of the tank with some nice rocks holding it down. I found out after this was all coated in cement that it was still VERY buoyant. Rocks were not going to be enough to hold it down at least not safely in my opinion. So I had to come up with a new plan and that was to silicone the new plexiglass base to the bottom of the tank. I figure that if I decide to remove this someday a mess on the bottom of the tank can be covered with substrate to hide it. works for me.

So this is where you have some options to think about and decide what you really what to do. I went with trial and error on this part so please read all of this and let me explain what I’ve learned then go from there.

Option A:
If you choose to silicone this right to the back of your tank, you need to leave the entire back of the background free of concrete come coating time. If you don’t the concrete will scratch the hell out of the back of your tank. I suggest taping off the back so if you get a bit on the back it will peel right off with the tape. I would use masking tape or any light sticking tape so that when you do peel it off it won’t take the styro with it.

Option B:
You can always just silicon the bottom of the background directly to the tank. Though if you do that I would suggest adding another piece of styro to the bottom of the base to make a “floor”. This will also give you more area to secure to the bottom of the tank then just the outside edge and inside cave walls. Be sure to go over the seems and cracks with the spray foam just like everywhere else. And again whatever is getting silicones to the tank must stay clean.

Option C: (my personal choice)
Attach plexiglass to the bottom of the base. (pretty much the exact same thing as option B)
I forgot to take pictures of this part and I apologize for that…
I used a piece of plexiglass that was about 6 inches larger then the background on the front and sides giving a good sized lip (since I had intended to place rocks there originally). In hindsight, a 6 inch lip almost all the way around probably isn’t needed, but I would suggest a few inches at least. (We’ll get to why in a second).

Put a generous bead of Silicone around the entire bottom of the base. With the background laying on it’s back, place the plexiglass on the bottom so that the plexiglass is even with the back of the background. (I suggest placing newspaper or something under this too before you do this) Give it a good push to make sure all the Silicone evens out and flip back upright. Some of the silicone will ooze out but that’s ok. no need to wipe it off or anything.

(this pic is from after cement coating but you should still get the idea)

This is optional but I thought it looked cool. Once the silicone has cured (about 24 hours) I went all the way around the bottom of the entire background (inside and out) with a couple generous beads of more spray foam. I figured it would get rid of the sharp corners and make it look like mounds of rock and such piled along the bottom edge just like I did for the edges of the walls and caves. This is why I suggested leaving a small plexiglass lip around the base of the background.

(Again sorry for the after coating picture but this is how it ended up looking)

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