Stock up. Keep a large supply on hand. You will be replacing this media at least once per month, depending on your situation. The Fluval U2 underwater/internal filter uses a total of five filter medias: 2 coarse foam, 2 poly/carbon pads, and 40 grams of ceramic bio-media. This is the one that you would need to replace frequently. The coarse foam can be rinsed out and re-used, being made of inert material. The ceramic bio-media can also be rinsed out, but should only be replaced if they are extremely dirty. I do not know how ceramic bio-media can get dirty enough to the point that they will need to be thrown away, but I suppose it can happen. Here's a potential scenario, if you used copper to medicate the tank at some point in the past, and now you want to keep invertebrates, then yes, you will need to replace all of the media in your filter. Even the ones that are considered inert, since even a small trace of copper can harm your shrimp. The Fluval U2 will run just fine without a poly/carbon pad installed. Set up as such, it will still function as a coarse mechanical filter and as a submerged biological filter. You just lose chemical filtration. This is an advantage to you during those times when you have to add medication to your tank. How well does this filter pad do its job? It does a fine job of filtering out smaller particles. These are particles that are too small be captured by the coarse mechanical filter. However, it does a poor job of chemical filtration. This is not surprising, when you consider that this pad does not hold granular activated carbon. Instead, one side of the pad contains bonded carbon. There is very little actual carbon in the product. What you have is carbon bonded to the filter material. Do not expect this filter pad to remove tannins from the water. It may remove a little bit, for a short period of time, but do not expect it to keep the water from turning yellow if you have driftwood in the tank. There may be enough carbon there to remove medication from the water. It is hard to review a filter media without taking into the consideration the whole system. The Fluval U-series of internal filters are excellent products. The smallest model, the U1, provides simple mechanical filtration. The rest of the series, provides complete filtration. So these systems can be a replacement for a hang-on-the-back power filter. The Fluval U2 will do a fine job of mechanical filtration, primarily because of this filter pad. But you do have to replace the pad often. If you are not too concerned about chemical filtration, you can replace the poly/carbon pads once per month. You can even alternate, by replacing only one of the pads, instead of both. I do recommend replacing at least one of the pads, every month. Mechanical filtration captures solid waste and puts them where they cannot be seen. However, please keep in mind that they are still in the water. The trapped solid waste in the filter pad is still decomposing within the tank, releasing nitrates into your water. Even if they are no longer in the water column, they are still in the path of the water circulation. The best strategy that I have found is to use a simple filter that is very easy to clean. Clean often. Remove as much solid waste from circulation as possible. This will help keep nitrate levels down and may help keep algae under control. This idea is also the reason why I have gradually replaced my canister filters with simple, HOB power filters. Many years ago, I kept some wild-caught pike cichlids. I was using a large Fluval 403 canister filter. My routine back then was to put as much media within the bucket/canister as would fit. And then only open the canister for maintenance every 3-4 months. After all, the service interval for canister filters are long, right? Sure, the canister will hold a lot of waste, but just because it's in the container does not mean that it is no longer polluting the tank. You are better off spending your money on a modest filter and cleaning it out often, rather than spending a lot of money on a filter that you will not clean out often. Am I saying that simple and cheap are better than a pricey canister filter? No, not at all. My point is, whichever filter type you choose, to clean it often. If you want a canister, and you are willing to go through the hassle of cleaning it once a week, then you have the best of both worlds. I suspect that most people would be more consistent in monthly filter maintenance if it were simple and easy. While an internal filter like the Fluval U is not as easy as your typical HOB power filter to clean, it is still easier than a canister. And having pre-made filter media makes the job even easier. Stock up on the replacement filter pads. Replace them often. That is an easy way to remove solid waste from your tank. This is a much better maintenance practice than letting the waste accumulate. You can make it even more convenient if you buy the pads in larger quantities.
