Overflow Tube Has Air!

[sduda]

I have an overflow tube on my tank feeding my sump. I have had the tank setup for over a year now and all has been well. I recently have started having problems with air getting into my overflow tube and causing the siphon to slow down which starves my sump and thus causes air bubbles as a result when my pump cavitates because of the waterflow slow down. Does anyone have any suggestions please?

 

[broomer5]

Get a pump with a higher gph rating.
If air is becoming entrapped in the siphon tube, there's a very good chance you don't have enough water flow to push the air through the U tube.
You say your system is a year old. Is the return pump the original one you had all along.
If so it may need a good thorough cleaning, it may be losing efficiency. Tear it down and check the impeller for damage, and clean it well with warm water and a small nylon brush.
Do you have a valve that may be throttled back some, restricting the output from the pump ?
Is your pump actually cavitating or just sucking in air due to low sump water level ?
What size pump are you using, brand and flow output ?
What is your overflow rated at in gph ?
How old is your sponge prefilter ?

 

[sduda]

It is a CAP 2200. It is the original pump. I just changed the sponge filter thniking this was the issue but no luck. The pump does have a valve to control flow but it is 100% open. The tank/sump has enough water because the water is up to the tip top of the tank (touching the glass top). The overflow tube is clean as a whistle so I know it is not restricting the flow. I could not tell you the pump rating in GPH or the overflow GPH. It is what I purchased from my LFS when I first got started. I appreciate your assistance. I am cleaning the pump again just to be sure it is perfect!

 

[luke]

Some people have hooked up a power head inside the tank for circulation, and used a venturi fitting that connects to the top of the siphon (you have to drill a hole and glue this tube in). That way when air gets in it imediatly gets blown into the tank. This is better than having the pump run dry because you have a siphon problem (don't let the pump sit, while blowing air, it overheats the pump and ruins it.) This has the added advantage of re-priming your siphon if it fails after a power outage.
Luke

 

[sduda]

Just when you thought you were doing something smart... I was cleaning the pump to ensure that it was not under performing, (it is a CAP2200), and I was brushing it off under luke warm water, pulled the impeller out, stuck my finger in where the impeller goes only to break that darn shaft off 1/2 way down! It seems to be functioning so far but it is just my luck... Any suggestions of a pump that I may want to consider replacing this one with?

 

[broomer5]

Bummer Stan ... sorry to hear that
I use a Cap 1800 for mixing saltwater batches.
The pump curve for a 2200 says
590 gph at 3 feet of head
550 gph at 4 feet of head
Again not knowing what your overflow is rated for makes it tougher to pick a pump.
A Mag 7 will put out
480 gph at 4 feet of head
A Ma6 9.5
800 gph at 4 feet
The Mag 7 would be my first safe choice not knowing anymore about your overflow.
Sorry about the Cap shaft.
BTW - are you saying your sump is filled to the very top as well ???
Not much room for drain back from the tank upon powerloss. Maybe I am missing something here ??

 

[sduda]

Sorry, I should be more clear. The sump has plenty of space for overflow. At the present time, the water level in the sump is just below the normal fill line (about 3" full out of 12"). I knocked the tube several times and the air has been some what reduced. At the moment, the airbubbles have gone away because the flow is increasing from the tank to the sump based on reduced amount of air in the tube. The pump is still functioning fine believe it or not. I am assuming that that shaft is there more for keeping the impeller centered because it does not actually turn. Finger crossed until I can get a replacement pump. I do appreciate the technical information, thank you.

 

[broomer5]

good luck

 

[von_rahvin]

i like the mags better. why?? i have never had a problem with one. I have used mags caps and rio's. all from different stages in my fishtank life cycle. at my curent stage i really like mags, the are quieter IMO, but i believe that i am starting a new place. I am just beginning to learn the joys of external pumps.