The AQUANEAT Aquarium Bio Sponge Filter is designed to sink to the bottom once you put it in your fish tank, where it will then start to mechanically filter debris from the water column while also provide biological filtration.
If this product isn’t sinking down the water column, then you can take a look at this troubleshooting article at Aquarium Blueprints to see how you can potentially fix this problem.
1. To start off, make sure that the base of the product is properly attached as it will help weigh down the sponge in water. Otherwise, this product will be too lightweight and may stay afloat in the aquarium.
The AQUANEAT Aquarium Bio Sponge Filter should already come with the base pre-installed when it was shipped. With that said, you may have removed the bottom and forgot to put it back on when cleaning the filter.
So, if you left the base off, make sure you find it and then re-installed it to the sponge so that it will be weighted down when put into your fish tank. This is especially true if you have a smaller version of the AQUANEAT Aquarium Bio Sponge Filter as these are extremely light in weight without any water.
2. You should also give the sponge some time to get waterlogged in your tank water. The added water weight should help the filter be weighted down.
3. If the airline tubing isn’t long enough, then it may be suspending the AQUANEAT Aquarium Bio Sponge Filter. In this case, you need to get a longer tubing so that the filter can comfortably rest at the bottom of your tank.
4. Last but not least, you can try placing a rock, piece of wood or décor on the filter in order to weight it down. You can either put the object at the top of the sponge or on the base.