I gave this 5 stars, because as nano skimmers go (and I've tried 4) this one is the absolute best, even if it took a while to adjust, and even though I made a few mistakes at first. So I'm grading on a curve :) FIRST: Don't make the same mistake I did! I have a Fluval Evo 13.5, so I read the instructions too quickly and thought I didn't have to install the brackets that hold the skimmer front and back housings together (the front and back of the skimmer split open so you can clean it easily) because it was already sized perfectly for my back chamber. But, NOT installing these pieces made the skimmer really loud because the skimmer pump caused those pieces to vibrate against each other. Once I realized the issue, it was too late; I had already thrown the other extra pieces away. So I ordered another one, just to get those two pieces--they're that important! Once installed, the skimmer quieted way, way down, and in about 2 weeks, it got even quieter when it broke in (it's at about 15db, 4 feet away, measured with an app on my phone). One thing to tweak, though, is to make sure the skimmer is seated as far back against the tank's back glass as possible (away from the tank's display/overflow), so the front inlet has enough space to draw in water from the tank's overflow. I used a piece of air tubing and slid it in between the skimmer and the front of that back chamber, just to push the skimmer away from the tank overflow. That was the trick to get it to start skimming properly. Once I further tweaked water level in the chamber (the largest knob on the top) and opened the air to about 80% open (the smallest knob on the top), it skimmed super efficiently, was quiet, and I've been super happy with it. [Hack: to set the air at the right level, close the small knob all the way counter clockwise, then open it clockwise about 2-3 twists of your fingers.] You'll want the water level/surface turbulation happening right at the bottom of the collection cup. If the tribulation is happening IN the collection cup chamber, it's too high and you'll skim too wet, and it will probably overflow in no time; back it down so the water line/turbulation is exactly level with the bottom of that cup. It won't produce skimmate immediately. Give it a few hours to start producing those large bubbles and skimmate). The hardest part was getting it dialed it. But once that's done, you don't need to touch it again. When you do water changes or pour something in your tank, it will stop skimming for a bit--don't touch the dials! It will start producing skimmate again in couple of hours. Once you've got it dialed in, you'll be impressed. I sure am.
