Deltec skimmer bubble break height in neck changing | D-D The Aquarium Solution
Question: 

Hi Tony,

 

I have an annoying issue with my Deltec SC 2060 skimmer and I’m hoping you might provide some insight. It’s been running for a year now.

 

I adjust the fine bubbles to not go above the neck. I’ve uploaded a picture of exactly where the fine bubbles stop. https://s20.postimg.cc/i6w6lqyfh/Skimmer_Picture.png

 

Almost two weeks goes by and the skimmer cup fills up a little less than half the cup. The water is dark.

 

Turn off skimmer, empty the cup, and clean it with tap water.

 

Start skimmer back up. The fine bubbles are now 1/3 to 1/2 up the skimmer cup. I wait 4 to 5 hours hoping the fine bubbles will come back down. It never happens. I rotate the water level adjust counter-clockwise until the fine bubbles are back to where I want it.

 

I have repeated this exact process for the past few months now. For the life of me I cannot determine why I need to do this. Why don’t the fine bubbles stay where they are at after each cleaning? I have also confirmed that the water level on sump is not rising as I know this can cause it.

 

Can you think of any reason why this is happening?

 

Thank you

 

-Arthur

Answer: 
Dear Arthur
 
I think the reason maybe two fold
 
  1. The surface tension of the water in the neck will be affected after the neck has been cleaned, typically the foam level will start to recover after a few hours however as the surface tension settles again and the clean surfaces start to become coated with fats and lipids.
 
2. The venturi pipe stub at the pump inlet can start to build up hard salt deposits and calcium carbonate at the air/water interface , when the venturi start to become partially blocked ( like an artery) the rate of air-water the pump pulls will change to the bias of water and this will affect the level inside the neck as the volume taken up by the air in the body will decrease. 
 
When you turn the pump off for cleaning some of the deposits will be dissolved or flushed out when the pump gets turned back on. This will alter the bubble break height in the neck due to the change in water-air ratio. Once the surface tension has settled you will notice a change in the bubble break height and adjust the skimmer.
 
 Over the next couple of weeks the venturi will start to block again but the slow change in bubble break height wont be obvious due to the time between setting the height last, the slow change in height and the dirty cup neck. You then turn the pump off ,clean the cup and the cycle begins again.
 
Try removing the venturi and giving it a good clean out with a drill bit around the same size as the internal diameter of the venturi pipe by hand and see if the bubble break height remains more stable , if the build up is regular ( this can be different from tank to tank depending on water chemistry / Ca/Alk dosing methods) you may have to do this with every cup clean to maintain the bubble break height.
 
Best regards Tony