RE: difficulty tuning skimmers! Most are not difficult to tune but there are some exceptions (poor design/ air to water imbalance etc..) . I prime all my new skimmers after 24hrs with a few drops of skim taken from my old skimmer before it's removed. I usually will only give a new skimmer a wet wipe down and not run them in vinegar over night, since I've seen no measurable difference in speeding up breakin'. I always start my skimmers with the effluent (output pipe) adjusted wide open so the internal skimmer water level is at it's lowest point. I'll let it run like that for at least 24 hours then adjust the water level to where the foam breaks about an inch below the collar where the cup attaches to the body. Shortly afterwards i almost always will see an air/water line (separation of turbulent bubbles below and a line where calmer bubbles start traveling uniformly upwards). That's when i seed it and the skimmer will drastically change from a struggling foam head, to a calmer, pillowy foam head. After that i monitor it, but do not adjust. Usually a day after that, i can then slowly raise the internal skimmer level in small increments (monitor for around an hour between adjustments) until a get the foam head where i want it. Note! Remember never to adjust a skimmer (especially a Hang On Back) so it produces wet skimmate right away. The skimmer isn't broken in yet and when it starts to break in, it will usually overflow and dump a mess all over the floor behind the tank. Sump skimmers are more forgiving but overflows can create breakin' delays and messes as well.