River Rock Cave Grotto Aquarium Background

I recently purchased a new 120 gallon aquarium and after looking at various options for backdrops, I couldn't justify the costs of most of them and most of the DIY backdrops were too messy and would have required too much time. So I decided to go ahead and install the same type of background I had used in my 60 gallon aquarium 6 years ago. Sadly when I went looking for the old plans on the internet, the original site I had found them on no longer existed and the forum post I also used for reference no longer contained images. Luckily I remembered for the most part how I had done it so I dove in and started working on it.

Link to original forum post I got my inspiration from.

https://www.cichlid-forum.com/threads/fixed-grotto-background-on-125-with-pics.232351/

• "Contemporary" Half Round (U shaped) Gutter - I found mine at Lowes and it comes in 10 foot lengths for around $11 US. Make sure you get the Contemporary gutter, a cut section is shown in the image above and not the K style gutter. I ended up using 4 lengths but needing only 3. $33
• Black aquarium safe silicone - It needs to be 100% silicone. You can use clear but the black hides better. I chose ASI Aquarium Silicone Sealant found on Amazon at $13 a tube. I have read other people have used other silicone sealants but I haven't tried them. I used 3 tubes, but only needed 1/2 of the third tube. I probably could have made due with 2 but... $39
• 11" black nylon zip ties - I found these at Lowes also in a 50 pack for $9. The 11" ties are needed to make the carrying handles. $9
• Krylon Fusion spray paint - Once again Lowes. I used 2 cans of satin otter brown at $4 a can. I kind of wish I had used satin black but it still looks good. But the black would have blended into the background better. $8
• 48" Lead Wire (optional) - Search for 1-Pound Roll 1/4 inch lead wire on Amazon. This can be used to attach the background to the fish tank. $9.50
• River Rocks 1"-3" - I found mine at the local landscape supply for $15 a bag. I ended up needing 3 bags to find enough larger rocks. It is kind of a crap shoot on the sizes of rocks you will get. I ended up with 2 5 gallon buckets of smaller rocks left over but we are redoing our yard so it wasn't a complete loss. $45
• Sandpaper
• Box cutter
• Saw of some sort
• 5 gallon buckets
• Paper towels
• Shop scissors - Do not use your wife's "good" scissors and do not ask me how I know.
• Fiberglass windows screen (optional, see below) - I had some laying around so unknown cost.
• Tin Snips (optional)

• Measure the interior dimensions of your tank. Mine ended up being around 71.5 inch long and 22 inches high.
• Decide how high you want the grotto wall to be. I wanted mine to be around 1 inch from the top, so each section of gutter needed to be 21 inches.
• Determine how many gutter sections are needed. The gutter is around 4.25 inches wide, so the most I calculated I could fit was 16, with 4 inches left over.
• Determine how many section per gutter. The gutter from the store comes in 10 foot, or 120 inch, sections. Dividing 120 by 21, gave me 5 cut sections each. Which at 16 cut sections needed, meant I needed to purchase 4 gutters from the store.
• Determine how many panels you will make. Unless you are installing into a small tank, you will need to connect multiple gutter sections into panels in order to install. I would suggest making panels of 5-6 segments if possible. The fewer panels the easier it is to hide the seam between them. However the more segments in each panel, the heavier it will be and the more difficult it may be to fit between the aquarium wall and any bracing. When determining how wide a panel can be to fit between the wall and the bracing, factor in the 2 (or more) inches that rocks may add to the panel width. I was originally going to go with 3 panels, 2 of 5 segments and one of 6 segments.

NOTE: The images do not exactly match the steps. The steps below are how I would do it if I could do it again, namely making all cuts and holes prior to painting.

• Cut the gutter to length. 6 years ago, cutting the gutter with a circular saw was a tad bit of a pain, so I decided to use a miter saw. Luckily I decided to research cutting vinyl gutter and came across a pro-tip. Reverse the blade in your saw so the teeth are backwards. That way the teeth are "melting"/slicing their way through, instead of chewing their way through. This made cutting the gutter much easier and I am sure would have made cutting it with a circular saw easier too.
• Dry Fit the cut gutter. I had the new tank in the garage so I could paint the back black. I just laid the cut gutter on top to make sure I hadn't messed up the measurements.
• Drill cave holes in gutter. The first time I did this, I just cut 2 1/2 inch holes. This time, since I had the bits, I cut 1 1/2", 2" and 2 1/2" holes and made sure they were offset to make it harder to see the individual gutter sections. There is no real rhyme or reason to their placement, other than to try and keep them from lining up horizontally as much as possible. When you drill the cave holes, lay out out the gutter segments next to each other and number them. That way you can see how the holes play off of each other and you can assemble them in the same order.
• Cut an angle so the gutter clears the tank silicone (Optional). - Cut off what will be the bottom back corner of each section of gutter. This is optional but it helps the gutter sit flush with the bottom. The cut doesn't have to be drastic or accurate. I used an angle grinder with a cutoff disk to cut a section 3/4 inch tall by 2.5 inches long, give or take.
• Drill holes in side for attachment. The gutter segments will be attached together with zip ties, so choose a drill bit a little larger than the width of the zip tie. Then clamp two segments which will go together and carefully drill 3 holes down the common side. The hole nearest the top should be 3 inches from the end, you will be making a handle using this hole. Since these holes will be used to attach the segments together, you do not need to drill holes on the faces facing the outside of the panels.
• Sand and clean up the gutter. In order to help the paint stick to the gutter, you will need to rough it up by sanding it. I went with 80 grit sand paper, since that is what I had, but 120 grit should work also. At this time, you should also clean up the edges of your cuts and the holes you drilled in the gutter.
• Spray paint the gutter. I ended up doing 5 coats and also made sure that I painted the cut sections of the holes. I didn't do that in my old tank and it bugs me that from certain angles you can see the while of the cut holes. The Krylon paint supposedly fully cures after 7-8 days, so I let it cure for a week before I started the next part.

Now it is time to make the panels, which is fairly simple.

• Connect segments together - You will use the zip ties and the holes you had previously drilled in the sides. Lay the segments out according to the numbering you had applied earlier and tie them together. Don't forget to trim off the excess zip tie. I also made sure that the cuts part of the zip ties would be facing the back of the tank.
• Make handles - In order to make these easier to move and to help with attaching the panels to the aquarium wall, thread 2 zip ties through the top holes according to the first picture above. Then zip tie them together. You will want to double up the zip ties to cut down on the chance that the weight of the panel will cause the zip ties to fail.

I am not 100% convinced that this step is needed. From my experience, very rarely do my fish use these caves as permanent dwellings, but mostly as avenues of escape or as places to hide as they get adjusted to the tank. So individual caves may give the hiding fish a sense of security, but they can also cut off escape routes if a picked on fish is pursued into the cave. Since I had done so on my first grotto wall, and since I had the screen on hand I went ahead and made individual caves. Some with only 1 entrance hole and some with 2. But you can probably skip this step and will never know the difference.

• Cut template from paper - Using the end of a scrap piece of gutter I made a paper template that was just a little bigger that the outside of the gutter.
• Cut a strip of window screen - I cut a strip of window screen about an inch wider than the template.
• Fold up screen strip - In order to allow me to cut multiple screen inserts at the same time, I folded the screen strip so that the template could fit on a folded segment. I forget exactly how many, but I believe it allowed me to cut at least 15 at the same time.
• Cut screen inserts - This is where the warning about using your wife's good scissors comes into play. Do not use them and if you can't control yourself, at least don't do it at the kitchen counter in plain view.
• Attach inserts - Using the silicone, attach the screen inserts to the inside of the gutter. You don't have to turn every hole into a cave, just do what you feel like. This step is messy so have paper towels on hand.

After you have attached the inserts, you are going to want to give them time to set up, at least somewhat, before moving on to attaching the rocks. You could probably get away with letting it cure for an hour or two, but since I did this step at night after work, I let mine cure for a full day.

You are going to need space for this step. You will need at least enough space to lay out two of the panels side by side, as well as enough space to dump a good quantity of rocks to allow you to sort through them to find the perfect rock. Think a jigsaw puzzle with no guarantee the pieces will fit. Luckily I had a work bench for the panels, and I used a 4'x4' scrap piece of plywood to dump the rocks on. This step took by far the longest amount of time. I spent 8-10 hours on applying rocks, mostly because i was looking for the right rock to fit any particular space.

• Rinse rocks - The rocks will come dusty, so you will need to rinse them off an allow them to dry. I poured mine into a 5 gallon bucket and ran water over them a few times. Once I had dumped all the water out, I dumped them on the plywood to finish drying.
• Sort rocks - I pulled out as many of the bigger rocks, 1.5 inches and above that I could find and set them to the side. You will need as many of these as you can find to span the gaps between the gutter segments. You will also use some of these to frame out the gutter holes. I also threw any rocks that were over 1.5 inches and thicker than around 1.5 inches in another bucket. I was concerned they would look out of place and also would be too heavy for the silicone to hold up. I ended up using a few of the smaller ones on the sides.
• Lay panels next to each other - Because you will be applying rocks to hide the seam between two panels, you will want to go ahead and lay them next to each other.
• Apply rocks - I started applying rocks to the outside of the left panel, by putting a dab of silicone on the back and pressing them on. The only real rule to applying rocks is to leave as little free space as possible. For the gaps between the gutter segments, try to use rocks that span the gap. If you don't have the right big rock, then you can have rocks that span only part of the distance, but may have to use another rock to hold down the glued side while it cures. If you look closely at the first picture above, you can see that is what I was doing.
• Apply rocks 2 - Where two panels meet, the method for covering the seam is the same as for covering the gap between panels. But you will want to make sure that you only glue down one side of the rocks and that you place them so that rocks on the two panels can slide into each other and hide the seam. The second picture is of a dry fit of two panels and you can't tell where the seam is.

I have read that silicone needs to cure 48 hours to become aquarium safe, however because I wasn't in a real rush and I had finished applying the rocks late Sunday night I gave mine more. It ended up being 6 days before I installed the panels and another week before I added water.

For the installation, since I have a 3d printer, I designed and printed custom clips to hold the background on. Because they were custom designed for my tank, I haven't included them in this instructable. However you can use the lead wire to attach the background to the aquarium. The background requires very little horizontal force to hold them in place.

• Prep work - If you are installing in an existing aquarium, you will need to drain around 25% of the water to allow for water displacement. You will also need to clear out enough space in your substrate so that the panels will with on the aquarium floor.
• Attach lead hook - Cut a 6-8 inch pieces of the lead wire and attach one end to the each of the zip tie handles
• Install in tank - Once you have maneuvered the panel into place, bend the other end of the wire over the top of back of the aquarium. You can then bend it to help hold the panel tighter to the back wall. I would also take a 2 inch piece of lead wire, bend it into a U and use it to clip the panels together. This will keep the panels from separating.

I have included the two pictures above to illustrate a few things.

• First picture
• This picture is one I took of the background of my 60 gallon tank that I made 6 years ago, prior to moving the fish. It has held up fairly well with only a few rocks falling off.
• It does not have a clip holding the two panels together and you can see they are separating.
• I wasn't as diligent about rock placement at the edges, so you can see where the two panels meet

• Second picture
• Part way through the build I had second guessed myself and went with 15 gutter segments instead of the original planned 16. I was thinking I it would be a hassle to put the filter intakes behind the background. I regret that decision, as I don't like the way the black background reflects of the side walls. I am hiding it with plants but I wish I would have put the intakes behind the two end gutter segments. I may fix that at a later date.

There are a couple of other things I would change.

• Use satin black instead of otter brown to paint the gutter. Though it doesn't look bad, I believe the the black would have helped the holes and gaps between the rocks blend in with the black background better.
• Paint the inside of the gutters. This probably really isn't necessary, but if you look at the background from certain angles you can see white peaking through the holes. Not a big deal, but.........