This is probably the most difficult part of building your ecosystem. Small fish are delicate and easily injured. The key to all of this is to be relaxed, understand the steps below, and move quickly but carefully.
Method One: Bag Method (recommended)
1. |
Your fish will likely come in a plastic bag. Carefully empty most of the water from the bag into your ecosystem or into a large bowl. |  |
2. |
When you have just the fish and a few inches of water, cut away the top half of the plastic bag. |  |
3. |
Make sure there is enough empty space in your ecosystem for the water left in the bag. Then tuck the bag into the top of the bottle. |  |
4. |
Carefully but quickly, pour the fish and water into the ecosystem. If there are plants sticking out of the water, make sure the fish didn't get stuck on them. If it did, pour in some water from the bowl to free the fish. | |
5. |
If the fish is still in the bag, pour water from the ecosystem back into the bag and try again. | |
Don't put the cap on just yet. Let the ecosystem sit out for a day to adjust. Then, in the afternoon, put the cap on.