Water tension

[Shawn_epicurious]

I have a question I have been curious about for awhile now. 200 gallon tank, 40 more gallons in the sump.

Every day right after I feed, my two return lines start blowing bubbles... not bad, aerates the tank a bit, stops after 30 minutes or so. I’ve watched my skimmer. It’s not “really” picking up more water... a little maybe. My return pump has the lowest average water level in my sump. From what I can see, a little whirlpool develops above the intake ports on that pump.

But why does it do it only when I feed? Is something changing the water tension?

 

[Larry L]

What are you feeding? If it's something fatty/oily it's possible the food is creating a slick on the water surface that increases the surface tension just enough for the pump to create a vortex. Or, to cause your skimmer to pick up just enough extra water to lower the level in the return section by a fraction.

 

[Shawn_epicurious]

What are you feeding? If it's something fatty/oily it's possible the food is creating a slick on the water surface that increases the surface tension just enough for the pump to create a vortex. Or, to cause your skimmer to pick up just enough extra water to lower the level in the return section by a fraction.

I feed one square of the Formula 2 frozen mysis shrimp, a small squirt of refrigerated mysis shrimp (for my smaller fish and some good dry pellets. I also feed phytoplankton Once a week..ish... I’ll give my eel some dehydrated krill (rehydrated of course)

 

[Randy Holmes-Farley]

What are you feeding? If it's something fatty/oily it's possible the food is creating a slick on the water surface that increases the surface tension just enough for the pump to create a vortex. Or, to cause your skimmer to pick up just enough extra water to lower the level in the return section by a fraction.

FWIW, surfactants would lower the surface tension, making it possible to form bubbles more easily.

 

[Randy Holmes-Farley]

I have a question I have been curious about for awhile now. 200 gallon tank, 40 more gallons in the sump.

Every day right after I feed, my two return lines start blowing bubbles... not bad, aerates the tank a bit, stops after 30 minutes or so. I’ve watched my skimmer. It’s not “really” picking up more water... a little maybe. My return pump has the lowest average water level in my sump. From what I can see, a little whirlpool develops above the intake ports on that pump.

But why does it do it only when I feed? Is something changing the water tension?

Formula 2 contains a number of ingredients that are surfactants (like soaps) that lower the air/water surface tension and make it easier to cavitate and create bubbles. Lecethin, for example.