How to prepare a coconut shell for an aquarium.
If you strive to make your aquarium a living piece of wildlife at home, a coconut or coconuts will look very original in your tank, complementing thickets of live plants. Scattered chaotically across the bottom of the aquarium or arranged in a certain composition, coconuts look original and give the aquarium a tropical appearance. Making them is not difficult. To do this, you need to buy a few larger nuts.
Most often, the shell is simply placed on the bottom, used as a shelter for bottom-dwelling fish that need hideouts to build nests and spawn. Cut off one third of the nut with a hacksaw, then drain the liquid from the nut and use a knife, wedge by wedge, to separate the coconut flesh from the shell. Give the flat cut a jagged shape using pliers. You can improvise here by breaking off parts of the shell in the right places. To prevent the sharp edges of the opening from injuring the fish, file them down. In this form, the ready-made decoration will have a natural look. The entrance to such a shelter can be made with pliers, breaking off small pieces of the shell until the desired size and profile of the entrance are formed. This is, so to speak, the most traditional use of coconut shell, but by no means the only one.
Hanging flower pots are made from the shell. After all, it is no secret that in tall aquariums, some plants grow well only when placed near the water surface, where there is more light and less water pressure. Making such a pot is easy. A quarter of the shell is used for this. A blank is cut out of a 2-3 mm thick Plexiglas sheet according to its internal profile — this is the future back wall of the pot — and several peripheral holes with a diameter of 1-2 mm are drilled in it for water inflow. In the geometric center of the blank, another hole must be drilled, the diameter of which is slightly less than or equal to the diameter of the suction cup’s cylindrical protrusion (it is desirable to have a retaining rim at the end of the protrusion). All that remains is to put the suction cup in place and secure the Plexiglas blank in the shell with epoxy glue. Now it is ready for use.
However, if you want the item to look as natural as possible, I advise tinkering a bit more with the neck of the pot. Formed by a hacksaw blade, it has too regular outlines. It is recommended to slightly “ruffle” it with pliers, giving it some unevenness — and the pot in the aquarium will look much better. Even when filled with gravel, such a pot is not very heavy, and a single suction cup is quite enough for its secure fixation on the aquarium wall. It is convenient to put fertilizers in such a pot, and remove plants from the aquarium for maintenance. You can also create compositions from several nuts as far as your imagination allows.
And one more remark about sawing coconuts — you haven’t forgotten that a coconut has three depressions at the end, one of which is pierced into a small hole? So, if you plan to use the coconut as a cave, saw off this exact end when cutting. Otherwise, a situation may arise later where small fish will try to squeeze through this hole and get stuck there. But if you plan to use the coconut as a pot for plants, then it is advisable to leave the hole — you will have ready-made drainage, less drilling!
To strip or not to strip the coconut on the outside is generally a matter of taste. Some people like coconuts bald and smooth, while others like them wildly hairy in all directions. There is no harm from the coconut’s “increased shagginess,” and it looks beautiful. Over the years, the coconut will go bald anyway (Ancistrus are hard at work!), and to my taste, hairy coconuts have a wilder look. But if desired, you can always go over the shell outside with a knife and polish it to a shine!
How to prepare a coconut? Naturally, it needs to be cleaned of the inner nut flesh. To do this, the coconut needs to be cracked somehow. It is most convenient to use a hacksaw and a regular hammer with a chisel when splitting a coconut. Sometimes, when you want to do something unusual with a coconut, a drill with a special hole cutter bit is used. Each coconut has three film-covered holes on its “bottom”. If you shake it, you can hear something sloshing inside the coconut. Such a coconut is fresh, it can be eaten. If nothing happened inside the coconut after shaking, it means it has been on store shelves for a very long time, and most likely dried out or, worse, soured.
So, returning to the coconut’s “bottom”, the holes need to be opened either with an awl or another hard, sharp, but thin object in order to pour out the contained liquid. By the way, you can drink it. After the liquid is poured out, we start processing the coconut. You need to decide how you would like to see the coconut in the aquarium: as a house or a boat. Because sawing the nut in this case needs to be done differently.
If as a boat, it is easier to saw the coconut along the wall connection line. If as a house, you need to cut off the “bottom”. If you need uneven shell edges, i.e., irregularly shaped pieces of coconut walls, make cuts in the places you need, insert a chisel into them, and use a hammer. Then the coconut will split chaotically.
The coconut shell is very strong and has a thickness of 3 to 5 mm. When deciding what the hole size should be, large or small, you must immediately take into account that later you will still have to pull out the nut flesh. And if the hole is very small, doing this will be extremely difficult. What is the easiest way to scoop out the nut flesh?
An option when you don’t need the coconut flesh. Having poked holes in the “bottom” or made small cuts so that air gets inside the coconut, put it in a plastic 
bag and put it in the warmest place in the apartment. In winter, this is near the radiator, and in summer you can put it in the sun on the balcony. You do not need to drain the liquid in this case. Being in a plastic bag, the coconut will begin to sour. The presence of juice will help the souring process quickly. The pulp in this case will be like porridge. This will take about 3-4 days. Now, having sawed or split such a coconut, the pulp can be scooped out with anything, either a spoon or a fork. And even if the sawed hole is small, such a soft inside of the coconut can be pulled out with a teaspoon. By the way, it is precisely when the pulp is like porridge, meaning it is most easily scooped out of the coconut, that you can use a drill with a special hole cutter bit. Holes like in a birdhouse are drilled with this bit. You can make from one to three of them.
You can resort to a longer, but reliable method of cleaning the coconut birdhouse. True, this method can only be used in summer. In a nearby forest, find an anthill, preferably of large red ants, and bury or place the pre-drilled coconuts on top. After “N” amount of time, the coconuts are cleaned to a shine. Such a coconut in the aquarium can be hung on a fishing line. It looks very original.
But if you still want to taste this exotic product, then it is advisable to extract the pulp without spoiling it. Scooping out the inside of the coconut is not as easy as it seems. Since 
it holds firmly to the walls of the nut shell. Using a knife, you can simplify the procedure of pulling out the pulp. If your kitchen arsenal includes a carving knife with a wide (not just thick) blade, make cuts in the coconut pulp from the edge of the hole to the center with the knife so that the tip of the blade is at the top. This way the knife will slide easier along the shell, plunging deeper into the pulp, and reach the center of the nut. The width of the blade is much greater than the height of the pulp, so the cut will be along the entire length, and the thickness of the blade in the pulp will make a groove. Having made the first groove, make a second one nearby so that they connect in the center. First, make cuts to the center of the nut’s interior, then try to make similar cuts in the pulp as if along a circle. That is, run the knife blade along the pulp like latitudes and longitudes on a globe, only inside the coconut. This results in squares that are easier to peel off.
With the help of this knife, we pull out a piece-slice of pulp. Peeling off these pulp squares is easiest by sliding the knife blade between the pulp itself and the shell. This is why the thickness of the knife blade should not be very thin; otherwise, you will simply bend the blade or just break it. At first, you will only be able to peel off the first rows of cubes closest to the hole. And it will get harder and harder to scoop out the pulp going deeper into the coconut. We perform this operation with grooves and slices until we pull out the entire inside of the coconut. You have preserved the nut pulp in decent condition, which can later be used for food, and freed the shell.
The coconut shell is soaked in water until it completely sinks to the bottom, boiled for 1-3 hours, and dried. Fibers are cleaned off with a file and coarse sandpaper, the core is removed by sawing with a thin saw, and then it can be glued back together. Holes are burned through with a rod heated on fire. The coconut is best sawed with a hacksaw, making 2 longitudinal cuts from the blunt apex to the pointed one. Then you need to pick out the soft seed with a narrow knife or screwdriver. The shell does not need to be boiled, burned, or soaked, and rags can even be left on it. But you must thoroughly scrape out the remaining pulp, sand the inside, and rinse it.
Despite the fact that the nut shell does not significantly change water parameters, you never know for sure where and under what conditions it was stored, how it was transported, and what it was treated with. Therefore, it is better to soak the shell in constantly changing or running water for a couple of weeks. The impatient can simply boil it. Common salt is not added. The water turns dark brown in the process. Drain the water, pour in fresh cold water again, put it on the stove, bring to a boil, and boil for 5 minutes. Thus, repeat the operation at least 3 times. Then, having cooled the shell to room temperature, we place it in the aquarium. A coconut processed in this way does not stain the water.
Do you know how to break pots? Shelters from other makeshift materials.
Grotto from “cold welding”. Self-hardening plastic. 
