Fluval FX6, trapped air---help me science this.

lojack

Hello All,

I have a one month old Fluval FX6. When it shuts off every 12 hours to purge, there's quite a lot of trapped air that gurgles out. It runs fine and there's no microbubbles that come out while it's operating.

I'm assuming the trapped air is making it work harder than necessary/less efficiently. There's no leaks and the inlet hose connects to the strainer(?) below the waterline.

After some research with Professor Google, it seems that the trapped air might be a result of cavitation. I thought perhaps there wasn't enough flow to the return pump with all of my old filter media crammed into every basket when I set up the filter. I've since removed all of that and it's basically running at "factory" specifications with the media it came with (plus the old bio rings I had). It still cavitates (I'm assuming) because there's quite a bit of air that purges every 12 hours.

The hose setup is my next best guess. I have the inlet hose as the "long run" at about 4' (it's a 6' tank) and the outlet hose is the "shorter run" at about 2'. I set it up this way assuming the return pump wouldn't have to work as hard pushing water 2' versus 4'. But now (based on my rudimentary knowledge of cavitation) I'm assuming the inlet run is creating too much resistance due to the length of the hose, causing lower pressure on the inlet side of the return pump.

I know what you're thinking, "why not just swap hoses and see if that solves it?" I thought the same thing! The way the stand is designed is there are two cabinets, one on each end, and I just recently finished "wire management." I would hate to undo everything and have it not solve the issue, haha.

TLDR: Does anyone think the length of the hose runs is the cause of my issue (trapped air that's purged every 12 hours)?

It's not a huge deal to me as it works and doesn't spew microbubbles constantly. But the filter also wasn't cheap (to me) and I'd like it to last as long as possible. I previously used a Fluval 406 for about 7 years and only changed because the deal on the FX6 was too good to pass up. Prior to that I had a 405 and also a 305 that never had any issues with trapped air aside from after regular maintenance of the filter.

Thanks for an ideas!

P.S. Wow that ended up a much longer post than I expected, sorry!
 

Tallen78

Hello All,

I have a one month old Fluval FX6. When it shuts off every 12 hours to purge, there's quite a lot of trapped air that gurgles out. It runs fine and there's no microbubbles that come out while it's operating.

I'm assuming the trapped air is making it work harder than necessary/less efficiently. There's no leaks and the inlet hose connects to the strainer(?) below the waterline.

After some research with Professor Google, it seems that the trapped air might be a result of cavitation. I thought perhaps there wasn't enough flow to the return pump with all of my old filter media crammed into every basket when I set up the filter. I've since removed all of that and it's basically running at "factory" specifications with the media it came with (plus the old bio rings I had). It still cavitates (I'm assuming) because there's quite a bit of air that purges every 12 hours.

The hose setup is my next best guess. I have the inlet hose as the "long run" at about 4' (it's a 6' tank) and the outlet hose is the "shorter run" at about 2'. I set it up this way assuming the return pump wouldn't have to work as hard pushing water 2' versus 4'. But now (based on my rudimentary knowledge of cavitation) I'm assuming the inlet run is creating too much resistance due to the length of the hose, causing lower pressure on the inlet side of the return pump.

I know what you're thinking, "why not just swap hoses and see if that solves it?" I thought the same thing! The way the stand is designed is there are two cabinets, one on each end, and I just recently finished "wire management." I would hate to undo everything and have it not solve the issue, haha.

TLDR: Does anyone think the length of the hose runs is the cause of my issue (trapped air that's purged every 12 hours)?

It's not a huge deal to me as it works and doesn't spew microbubbles constantly. But the filter also wasn't cheap (to me) and I'd like it to last as long as possible. I previously used a Fluval 406 for about 7 years and only changed because the deal on the FX6 was too good to pass up. Prior to that I had a 405 and also a 305 that never had any issues with trapped air aside from after regular maintenance of the filter.

Thanks for an ideas!

P.S. Wow that ended up a much longer post than I expected, sorry!
I’m running 2 fx6’s on a 155 and they do a self purge every 12 hrs it sounds to me that yes u have ur hoses backwards make ur intake short no slack loops straight from the canister up and over use the longer hose for ur return on the opposite side of the tank from ur intake
 
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Islandvic

I'm surprised you are not using both the FX6 + 406 on the 6ft tank.

In my opinion, I dont think it's an issue with the hoses.

I think air is getting sucked in somewhere.

I suggest to check all of the hose connections and also consider greasing all the orings/gaskets/seals with food grade silicone lube.
 
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lojack

I'm surprised you are not using both the FX6 + 406 on the 6ft tank.

In my opinion, I dont think it's an issue with the hoses.

I think air is getting sucked in somewhere.

I suggest to check all of the hose connections and also consider greasing all the orings/gaskets/seals with food grade silicone lube.
There’s plenty of flow and biofiltration for what I need with just the FX6. I originally was going to “hot rod” the 406 and add a small power head for circulation. But after buying replacement parts for the 406 and the power head I wasn’t saving a ton versus the deal I got on the FX6 lol.

I was going to buy some lube anyway so that’s a good idea. Even though it’s “water tight” maybe it’s not “air tight” at all the connections.
 
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lojack

I’m running 2 fx6’s on a 155 and they do a self purge every 12 hrs it sounds to me that yes u have ur hoses backwards make ur intake short no slack loops straight from the canister up and over use the longer hose for ur return on the opposite side of the tank from ur intake
Thanks for the suggestions. And yes, there’s no slack in the hoses (it’s my 4th canister... and as I re read my thread, 4th Fluval... I feel like a fanboy haha).
 
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Flipper747

Hello All,

I have a one month old Fluval FX6. When it shuts off every 12 hours to purge, there's quite a lot of trapped air that gurgles out. It runs fine and there's no microbubbles that come out while it's operating.

I'm assuming the trapped air is making it work harder than necessary/less efficiently. There's no leaks and the inlet hose connects to the strainer(?) below the waterline.

After some research with Professor Google, it seems that the trapped air might be a result of cavitation. I thought perhaps there wasn't enough flow to the return pump with all of my old filter media crammed into every basket when I set up the filter. I've since removed all of that and it's basically running at "factory" specifications with the media it came with (plus the old bio rings I had). It still cavitates (I'm assuming) because there's quite a bit of air that purges every 12 hours.

The hose setup is my next best guess. I have the inlet hose as the "long run" at about 4' (it's a 6' tank) and the outlet hose is the "shorter run" at about 2'. I set it up this way assuming the return pump wouldn't have to work as hard pushing water 2' versus 4'. But now (based on my rudimentary knowledge of cavitation) I'm assuming the inlet run is creating too much resistance due to the length of the hose, causing lower pressure on the inlet side of the return pump.

I know what you're thinking, "why not just swap hoses and see if that solves it?" I thought the same thing! The way the stand is designed is there are two cabinets, one on each end, and I just recently finished "wire management." I would hate to undo everything and have it not solve the issue, haha.

TLDR: Does anyone think the length of the hose runs is the cause of my issue (trapped air that's purged every 12 hours)?

It's not a huge deal to me as it works and doesn't spew microbubbles constantly. But the filter also wasn't cheap (to me) and I'd like it to last as long as possible. I previously used a Fluval 406 for about 7 years and only changed because the deal on the FX6 was too good to pass up. Prior to that I had a 405 and also a 305 that never had any issues with trapped air aside from after regular maintenance of the filter.

Thanks for an ideas!

P.S. Wow that ended up a much longer post than I expected, sorry!
I have the exact same problem. My better half (wife) is tired of the noice it makes when restating every 12 hours. Did you find a solution?
Need help!
 
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lojack

I have the exact same problem. My better half (wife) is tired of the noice it makes when restating every 12 hours. Did you find a solution?
Need help!
Sorry, I replied to your other post before seeing this.

Nope, never solved it.

I swapped the inlet and output, greased the orings and gasket, tried tightening and loosening the lid, didn’t seem to make a difference.

It’s been almost a year and it still purges a ton of bubbles after it does it’s 12 hour pause. Eventually I might try new hoses in case there’s a pinhole, but I doubt it since it doesn’t leak anywhere.
 
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