There are a few reasons why Orbeez are not a good choice for aquariums. First, they can disintegrate and release a harmful substance called polyacrylamide into the water. Polyacrylamide is toxic to fish and other aquatic life. Second, Orbeez can hold a lot of water, which can cause the water level in the aquarium to fluctuate. This can stress fish and other aquatic creatures. Third, Orbeez can block filters and other equipment in the aquarium, which can lead to poor water quality.
For these reasons, it is best to avoid using Orbeez in your aquarium. There are other, safer alternatives that you can use to help retain water and reduce the frequency of watering. These alternatives include peat moss, coconut coir, and vermiculite.