If you have fry or even small fish like Neon Tetra's and Guppies then you will want to hatch out baby brine shrimp (BBS). I keep my pre-mixed salt water in a gallon jug sitting on a seedling mat to keep it warm. I have two hatchers going at once because it takes two days for the shrimp to hatch below 78 degrees . I use one and have another brewing for the next day. I got that thing sitting on the base from Brine Shrimp Direct. It's a San Francisco Bay brand product. It does work good for hatching but it makes me nervous with the air attachment coming in from the bottom. I can just see a leaky mess at some unexpected moment . But one thing it is really good for is collecting the BBS. They gravitate down into the neck of the bottle and it is super simple to drain them out into a sieve or brine shrimp net . You could make one really easy by drilling a hole in the pop bottle cap that matches the airline tubing diameter and siliconing it in place. That's what the containers are. 2 liter plastic pop bottles. Cheap as it gets.