Bubbles On Screen Scrubber

I would point out that this build up of DOCs are also a food source for bacteria, and as far as I can tell are a speciality food for cyano and dino's. A bit controversial in a scrubber setting, I know.

 

Just a thought - most people run a scrubber, reverse lit to the display and also in a sump (as far as I can tell). So, when the main display lights are off and photosynthesis halts, the display organisms give out more Co2 than they are consuming. Where does this excess Co2 go ? Well, appropriate aeration of the display should liberate excess Co2 to the atmosphere immediately above the display and it should linger there (heavier than air). But it won't linger there because the overflow pipes that feed our sumps also provide an outlet for the Co2. Therefore the sump gets lots of this excess Co2 in gas form and it remains on the sump surface, until it effectively overflows or gets moved away. This gas is then incorporated into the water once again by the copious amounts of bursting bubbles on the sump. Another thought, if the size of the bubblescreen air inlet is shortened, to below the level of the sump lip, this gas could be directly used to enhance the Co2 concentration of the screen bubbles without artificial augmentation.

 

I actually replicated this effect last week. I thawed a bag of frozen prawns (I love prawn cocktail), then transferred the nutrient rich melt water to a cup. I fed 100ml of this liquid to the tank. Within two or three minutes my skimmer was going crazy and my sump developed a foam from the bubble screen which looks identical to yours. After 4 hrs skimming (with skimmer) the effect subsided and everything went back to normal. I know you have no intentions of skimming but a brief period of skimming may resolve your issue, or a bit of activated carbon may help.

 

Don't get any weird ALK consumption on mine, but I never have, as this aeration made sense from the beginning, and I matured the screen with bubbles going over it. That's not to say that every strain of algae will behave in the same way. I see you've got a control valve for the air, try turning it all the way down then increasing it till you get to the foaming stage, (Floyds suggestion also makes sense).

 

Do you consider the foam as a problem? Surely there just gonna break depositing the contents back into the water ? Or is it overflowing from the sump ?

 

What happens if you cut the bottom off a coke bottle, take the lid off and put the cut end over your scrubber overflow? You could put some coarse sponge in the bottle neck, to act as bubble remover. Bit rough and ready I know, but would save buying a skimmer and as always subject to very cheap alteration and improvement.