ive had a 26 gallon bowfront tank set up for about 6 months. im using the fluval 207 canister filter . its running great and ive had no casualties.i have healthy,active danios and mollies.i have 11 fish currently.. i am going to a 36 gallon tank and am wondering if i need to step up to the fluvall 307. the specs on the 207 claim it can filter up to a 45 gallon tank so i will use that unless i hear a contrary opinion from you folks. hopefully you can give me your tank size and which fluvall you are using . im currently using a spray bar off the fluvall which i have raised off the surface hopefully creating surface agitation.