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One method that will help protect danio eggs is to place a 2-inch layer of glass marbles at the bottom of a 5 to 10 gallon aquarium. Then fill the aquarium with water until it reaches about 1 inch above the marbles. This provides enough room for the adults to swim around, and a very short fall for the eggs to take to their safe place in the marbles. The eggs will then fall in between the marbles, where they'll be safe from the adults. These are not special marbles, just regular marbles you'd buy in a dollar store or toy store. Or, you can use glass "rocks" from a decorating store or Ikea that are normally used in flower arrangements or candle holders. The upside to this arrangement is that it's really easy to implement, as glass marbles are easy to find. The downside to this arrangement is that glass marbles have become expensive in recent years and this method may be more expensive then other methods. Another downside is that you have to "catch" the adults once they've bred, as they're not contained in one area. Another method to help protect danio eggs and babies is to place a breeder net inside the breeding tank. A breeder net is basically a basket that can be attached to the rim of the tank. The mesh of the basket allows the eggs to fall through, into the main part of the tank, but the mesh keeps the adults from being able to get to the eggs. Once the breeder net is placed in the tank, fill the tank with water until the bottom 1 inch of the breeder net is under water. When looking for a breeder net, make sure it's big enough to allow the danio eggs to fall through. You can buy a breeder net in most pet stores and aquarium shops. The upside to using a breeder net is that it's really easy to put the adults in the net and take them out of the net. You won't need to catch any of the adults in the main tank. The downside is that you have the find the right net for danios so the adults can't get through the mesh, but the eggs can. You can easily overcome this downside by asking someone at the aquarium store for assistance. A spawning mop is a bunch of acrylic yarn knotted together to form a mop-like contraption. For a 10-gallon tank, you'll need about 10 to 20 spawning mops. Place the spawning mops at the bottom of the tank and fill the tank with water that goes no further than a couple of inches above the top of the mops. The yarn will partially float in the water creating a protective area for the eggs, similar to seaweed. You can easily make your own spawning mops using the following instructions: Cut pieces of acrylic yarn to ~2 feet in length. Lay 2 dozen of these yarn pieces beside each other and fold the bunch in half, right in the middle. You should now have ~48 strands of yarn hanging down. Put a knot in the top of the bunch, where you've folded it in half, to hold all the pieces together. An upside to this method is that the spawning mops are homemade, usually with old materials you (or a friend or family member) has anyway, so you don't have to spend money on anything new items. The downside is that you have to physically make each mop. Another downside is that you'll eventually have to catch the adult danios when it's time to move them out of the breeding tank.
Use marbles to create a safe place for the eggs. Hang a breeder net to protect the eggs. Make a spawning mop out of yarn.