It won't be long before you find yourself trying to catch a fish in your own tank. Whether it needs to be isolated because the fish has become a bully, or is injured or sick, the fish will unlikely be willing to go without a chase. Because of the rockwork, and the delicate nature of the small aquarium space, hand netting may not be feasible. In these cases you can create a simple fish trap at home with a few supplies.
To start, you will need a clear container, A two liter soda bottle will work for most small fish, a larger container may be needed for larger specimens. (For larger fish the same ideas below will work, the trap will just need to be larger). You will also need super glue, and a good pair of scissors. Older round 2 litter bottles work better than the newer sleek bottles that look like 20 ounce bottles, like those used by the Coca Cola company.
First, remove any labeling and markings from the bottle. Rinse thoroughly, do not use soap. The container should be free of chemicals.
Second, cut the bottle in a circle as shown below. It should be cut where the "dome" portion of the top ends.
Third, cut a hole around the screw top making a hole larger than the fish you want to capture as this will be the entrance of the trap.
By now you should have two pieces, one 2 liter bottle without a top, and one top without a bottle or a spout. The bottom should look like this:
The top should look like this, except it should be clear I used a green two liter bottle for the top for illustration purposes:
Fourth place a thin line of super glue around the base of the modified dome piece of the two liter bottle.
Finally place the dome into the two liter bottle inverted, and allow the glue to dry. Poke a few small holes in the top of the two liter bottle trap, the bottom of your trap should be the area that has label remnants. When the trap is done, it should look like this:
To use your trap, fill the bottle up with water in your tank. Use the holes on the top to allow trapped air to escape. Place food for your fish inside of the trap, and place the trap on the bottom of the tank, preferably in an area the fish frequents. Now to play the waiting game. The fish will eventually wander into the trap, and because of the convex nature of the dome exit, the fish is likely to miss the opening, and swim down and to the sides, being trapped for at least a short while. Once the fish is caught remove the trap, remember where you have holes so you don't make a mess or spill the fish back into the tank.