Air buildup in canister filter

[Ichthyologist]

I am looking for suggestions on a particular issue I am having with my Fluval 405 canister filter. I have a (now) lightly stocked planted 75 gallon freshwater tank. Over time, the canister seems to develop air pockets in it. As a result, the gph seems to be affected. If I rock the canister around, I will get the "churn" sound it makes as it processes air through it.

I thought perhaps my tubing configuration might be the problem. The 405's output goes through a Turbo-Twist 12x-36 UV sterilizer before returning to the aquarium. I had the sterilizer mounted horizontally so that the 405's output went straight up into it, then on the other end it went out of the side before going back up.

I thought maybe the air was getting trapped in the sterilizer, so I moved things around so that it would be vertical and the flow would travel bottom to top. To do this, the 405's output goes back down to near the bottom of the canister into the sterlizer, where it then travels straight up through it and back into the aquarium.

Now I am positive the sterilizer is no longer the reason air is getting trapped, but the canister still develops air within it. I am convinced the gas is the toxic byproduct of the nitrogen cycle happening within the canister, because since this problem has started happening I have had massive fish deaths.

My last option seems to be to move the UV sterilizer one more time so that at no point does the water have to travel back down before going up again. It is just I am hard-pressed to believe that the 405 does not have enough power behind it that this problem should be occurring in the first place, but that seems to be a logical deduction.

The 405 contains only the filter pads and all the trays are stocked with bio-rings; no carbon.

Does anyone have any more thoughts before I dig into this once again?

 

[Gunz05gunz]

I get that on my planted tank due to the filter intake sucking up the bubbles coming off the plants. It burps once every 10 mins or so. Try checking that all your connections are tight. I have no experience with uv sterilizers so I can't help you there.

 

[neilanh]

i get that air build up in all of my rena canisters. Honestly, I just ignore it and haven't had any issues because of it. 5 canisters on 4 tanks, not a problem.

 

[metsfan421]

Experiencing same issue except mne stops pumping

I am experiencing the exact same thing except when mine stops it fully stops the filtration. If I shake the canister, quite violently, I hear the sound of the bubbles (air) inside the canister, and it will start filtering again. After 10-15 mins it stops again. Canister was just cleaned and new water added to canister before reattaching to tank. Any ideas what I can do to stop this? I do have some slack in the return hose to the tank. Could that cause it?

 

[Wy Renegade]

How far below the tank is your canister positioned? Most canisters are designed to sit at least 24" below the bottom of the aquarium. Sitting the canister filter too high can result in not getting enough water dropping down into the canister - just a thought.

 

[metsfan421]

distance

Its on the floor about 4 feet below the top of the tank. Its a 75 gallon and its a fluval 406 filter

 

[Wy Renegade]

Its on the floor about 4 feet below the top of the tank. Its a 75 gallon and its a fluval 406 filter

75 is close to a three foot tank isn't it - can't remember off the top of my head, but I would think that a four foot drop from the top would still be sufficient for the filter.

 

[metsfan421]

about that

It's approx. 3 feet long, yes. I have an eheim connected to it as well, doesn't have this problem at all. I wish Fluval products actually worked well. Anything else I could try? Would disconnecting the filter and then emptying the water out completely and filling it to the top help? I only filled it about 3/4 of the way when I connected it to the tank the first time.

 

[jrc0528]

Ok, the only way for air to end up in the filter is for it to be sucked in. There are several ways it could end up sucking in air...

1) you have an airstone too close to the intake

2) you have a CO2 diffuser too close to the intake

3) there are micro-bubbles getting sucked in along with the water

4) the intake tube in the aquarium is admitting air above the waterline

5) you have a leak at the hose connection to the aquarium intake tube

6) the intake strainer is severely restricted and causing the pump to suck air in though a seal somewhere.