Yeah sounds like its too strong. If you try to reduce the flow do it on the water return side.I have a 12 gallon long with an eheim 2213. I just stocked it with some rummynose tetras and noticed that they have trouble swimming against the flow created from the intake. Theyre constantly facing away from the area around the intake, they almost look like salmon swimming upstream. reducing the output doesnt seem to fix this, any ideas?