Tunze Skimmer 9005 hardly skimming

[Shoreline]

Hi all, I'm a long time reader of Reef Central but took the plunge and registered as I need some help with a second-hand Doc skimmer I purchased. The seller claims it is six months old but the amount of coralline on it makes me think it's over a year, it has the old style pump, not the present hydrofoamer (does anyone know how long the new pumps have been on the market?).
Well the skimmer didn't produce any skimmate for the first week and when I contacted the seller he said give it time, oh and he posted out the manual. Two weeks later I had had about an hour where the skimmer foamed over the lip into the cup, the rest of the time its about an inch over the water level. I dismantled the skimmer, cleaned and checked every part, including the impeller and bearings. All appear fine. I've returned it to the tank where its sat for another two weeks still not producing enough foam to fill the cup. I'm now in the middle of an ebay dispute to try to get a refund on this not nearly new skimmer. The sellers claiming it was working and I have damaged it by dismantling it! I suspect a fault with the motor block but any advice is welcome. My Aqua-medic skimmer was working fine and is still connected to the side of this 60g reef tank. I have mostly left it off but do have to run it occasionally when I fear that my tanks not being skimmed at all.

 

[rvitko]

The new models with ejet pump started to come in in March, the pump makes very little difference, the new pump is quieter and looks different, but in terms of performance there is no real difference. In a well run tank coralline can take over in a couple months, so I wouldn't use that as a gauge. How deep do you have it submerged and how far out do you have the air screw? Do you have the front shutter door completely open? A major pump issue is unlikely, the motor typically works or doesn't, technical problems are typically limited to needing a new impeller, it is possible yours is undersized as they are hand cut on a lathe, or having a silencer that leaks and takes in some water. However, most issues are as the seller said, a combination of many small errors in assembly and set up and maybe a minor technical problem, for example here is a common scenario-

Tank has a lot of free floating sediment from a recent overhaul, the sediment impedes skimming and restricts the venturi. Most people add a new skimmer as part of a fairly major tank overhaul so hands have been in the tank, detritus stirred up, water changed, etc. Additionally, the silencer pulled away and has a small hole where it was glued to the skimmer body so water is seeping in and reducing the air flow, this can happen in shipping. The skimmer is also not tuned properly so the air flow is too low.

This is typically what I see when these skimmers come back, many very small problems that if only one was present would reduce skimming but not stop it, but as a cumulation result in a complete lack of any skimming.