ok need an explanation on how this is possible.

[JMLenke]

Ok 20H that is planted with all the plants (well most of them) from the last meeting.

Dosed with Excel and other then liquid dosed following bottle instructions, nothing else. No Co2 added yet (need to get the tank refilled).

The only filtration is a Magnum 250 HOT "canister", with a small handful of crushed coral in the filter and nothing else.

After an hour of the lights on and then progressively more often through the light cycle the filter will look like it has a venturi connected. I have modified the adjustable outlet pipe so that it is pretty short. There are no leaks in the filter and I have reseated the gaskets a couple of times, any ideas what would be causing the filter outlet to be expelling air occasionally?

[Jamie G]

Great question, cuz my Eheim just started this little phenom too.

[B Considine]

Is it an Eheim 2213? Mine's been burping ever since I cleaned it out 2 months ago.

[JMLenke]

well jsut double checked and now that the lights are out (been out for about 3 hours) no aeration from the canister.

[RTRJR]

If the flow-through restricted or clogged? The pump could be cavitating.

[JMLenke]

nope not obstructed, I am wondering if it is cavitating due to the 3 90 bends it has to do to expel the water.

[RTRJR]

Cavitation come from pump starvation, impeding the intake. Exit back preesure normally is not an issue so long as there is positive flow at some reasonable fraction of the output rating.

[JMLenke]

Then why would it only cavitate when the lights are on and progessively more often until the end of the light cycle? Once the lights go out it stops.

Thats what has me confused.

[RTRJR]

Perhapos because that is the only circumstance under which your tank is supersaturated with O2 and so most likely to show cavitation? Cavitation is a physical effect on dissolved gases, it matters not which gas is involved - if O2 is saturated or supersaturated, it will be the one coming out of solution from impeller turbulence from starvation.

[JMLenke]

yeha maybe, just totally washed every bit of it out to see what happens. There was some debris on the filter pad so we shall see if there is a change.