Check that the airline is clear. There will often get to be calcification where the air meets the water in the venturi (the bell shaped thingy on the end of the pump). You should be able to remove the venturi and soak it in vinegar overnight. You can also pull the airline off and inspect that the opening is clear. A partially blocked airline will produce the effect you describe in your first post.

On another note, a person's opinion of the ability of a skimmer is directly relative to the other skimmers that person has used. If the person who sold you the skimmer never tried anything better then it is quite possible that he indeed thinks the skimmer "is very good". As with everything in this hobby, buyer beware - research potential purchases before purchasing. :)

Aha, good picture worth many words. Forgot to mention in my last post to check both outlet lines & adjustments for possible obstructions that may impede outflow & raise water level inside skimmer. Also, if yours has the foam jobs on the end of the outlets, remove them. No need & they will eventually clog & impede flow with similar results... overflow. Unless you clean them every couple of days...

Bwahahaha! Truer words couldn't have been spoken!

Skimmer problems solved and unit upgraded
 

Thank you all for your help,

Especially Mike and Myka. Your were on the money. The root cause was just what Myka said. When I took the unit out for a complete cleaning and upgrades, I checked the venturi. Just as Myka said the air intake in the venturi was blocked with salt/calcium. Clean that and now its is running great. In addition as Mike suggested I have now installed a valve on the inlet so I can control the inlet flow. Control of only the oultet can over pressure the skimemr leading to overflowing. Also I drilled and tapped the cup and installed a drain so if it does fill it will drain into a bucket and not over the floor. Thats a real plus for the wife :biggrin:.

So I hope this tread serves others in the future. This was a great learning. And I got to say I have a lot better understanding of what makes a HOB skimmer work. Still may in time go to a sump as I can see the advantages.

Once my tank settles down I will snap some picture to add to the tread as DIY upgrades for older HOB skimmers.

Cool, that Myka gets to the root cause of many things. I think you should add to her 'reputation'. You can do this by clicking the little scale icon next to the post #11.

Awesome! Glad I could help. :thumb:

Hey no worries about that, but thanks. :)