Tunze 9004 Skimmer - Not generating much foam. Bad pump?

[erikras]

I purchased a 9004 for my 20g frag tank a few months back. For the past few weeks it hasn't been generating enough foam to push anything over the top of the neck. I've taken it apart and cleaned everything twice, paying special attention to the air tube, silencer, and pump impeller. Nothing seems out of place. It worked fine for the first month or so then suddenly stopped creating much foam. Nothing else changed. Even with the air valve fully open I can only get the foam about half way up the neck of the collection cup. The skimmer is sitting in the sump so that the water level is about 1/2 to 3/4 up the intake slots on the cup and there's about 1/2" of clearance between the unit and the bottom of the sump for unrestricted discharge.

Any ideas?

Thanks!

 

[rvitko]

If it only houses some frags, it is possible the waste load is just very low and there is not much to skim. If the impeller looks fine and the pump is clean and you see no obstructions in the airline, I would assume the issue is too low of a waste load or some additive being used is interfering with skimming.

 

[erikras]

Roger,
Thanks for the reply. Even without much bio load, shouldn't I be able to get it to foam to near the top of the neck with the air valve fully open? For the first few weeks, I had to keep the air valve mostly closed to keep it from overflowing.

When this problem started a couple of weeks ago I wasn't using any type of additives in the tank. Just straight up salt mix right. Within the last few days I've started to dose the same Korallen Zucht (sp?) additives that I dose in my display tank. They seem to have zero effect on skimmate production of the skimmer in that system.

Thanks again!

 

[rvitko]

Not necessarily, the foam that rises up is a protein/ cellulose froth, it is not just the bubbles. If you look closely at a skimmer that is working you will see a foam of a different texture and color form at the top of the bubbles, it is usually yellowish and finer, essentially the bubbles are whipping a meringue and this is what has the consistency to rise without breaking. Enough of it has to be present to be whipped into a froth and make it up the riser. I think the best test to verify the skimmer is fine is to set it up in a tank that has a higher load that another skimmer is presently performing in. You will likely need to shut down the other skimmer for the test to be conclusive.

 

[erikras]

Roger,
Thanks again for another detailed reply! I'll place it in my (overstocked) 25g display tank and see what happens.