I just done a quick search on this filter and the older models have the flow adjuster and the newer ones don't. If it has a lever, I'm sure this is for adjusting the flow. You will NOT do any harm by setting it up and trying it. Some people like to over filter and over filtering is better than under-filtering. Danios are great fish and very hardy. They don't mind a strong current, obviously if it's like a whirlpool, I wouldn't use it but I honestly don't think it will be. When the filter is full with floss, it will reduce the flow anyway. Try it and see how you get on. Remember too, the 200 will do all the filtering you need, if you decide not to use the 100. The 100, is just a bonus. The 100 will NOT be used for housing BB, solely for mechanical filtration, so when the floss gets dirty, you can just remove it and replace it. Rinse it if you like but because it's SO cheap, I just replace mine. You can get the floss online ebay/amazon or in a crafts/hobby shop. A massive bag for a few dollars. It will last you years!!. Just make sure it's 100% polyfill, no additives-->Fire Retardants. In case you don't know the filter floss looks like Candy Floss, except white....lol