How can I hook up one Fluval 304 to two 20 gallon tanks?

[danger_chicken]

Not really danger. If the teeth/strainer in an overflow gets clogged the water can always spill over the top of the overflow and into the drain preventing the tank from overflowing. That is why the tops of overflow boxes are below the lip of the frame. There is no backup mechanism in a siphon. Also keep in mind that should for some strange reason, an overflow become completely clogged only the few gallons of water in the sump of the filter is going to overflow the tank. But since the intake strainers of a canister are most likely located near the bottom of the aquarium the result is that one tank will overflow and the other tank will drain itself down until the siphon sucks air. Consequently draining one tank and greatly increasing the volume of water spilled onto the floor.
Trust me. Filter design is part of what I do for a living. I know what I am talking about. But if you still don't believe me go ahead and try it. After all it's not my floor you will be soaking.
Andy

I appreciate you sharing your experience, that always gives me insight to things I may not have thought of - good or bad.

For the sake of friendly debate, what I'm getting out of your posts isn't that it wont work, just that there is risk of flooding. Assuming the flow can be tuned for this to work the next issue is potential flooding. One possiblity is dasiy-chaining the tanks together. I don't like the idea from a purely fitration point (intake in one tank, return in another); but as overflow prevention this could be more stable than a w/d in regards to flooding - if the flow through is sized correctly.

A large part of what I do for a living is identifying problems and then solutions for those problems. Since I haven't tested any of this its all speculation, but like I said I'm the adventurous type and this is Prince's project not mine . However, if it were mine I'd would test and develop it on a small scale and then go for it! :jumpy:

 

[AndyNarwhal]

I think the point I would make is that this is nothing new and people have been trying this since canisters first came out (including myself). And every time it will eventually fail. If enough people tell you that jumping off a cliff is a bad idea do you do it anyways?
If the filter causes the tank to overflow during normal course of operation then I would consider that a failure. There is just no way to make the real time adjustments necessary to keep the tanks balanced. However you do bring up a point that could make it work. If the tanks were connected with a siphon tube they would balance each other even if they had separate intakes and returns in each tank. As the water level dropped on one tank water would flow into it from the other tank. There is still of course an element of risk that the siphon would break. But with an Aqualifter maintaining the siphon it would work.
I still think it is a risky, complicated, and inefficient way to filter two aquariums but that is more opinion than fact.
Andy

 

[danger_chicken]

If enough people tell you that jumping off a cliff is a bad idea do you do it anyways?
Andy

Hell yeah that sounds fun! But really, it would depend on the people and the cliff My gandmother would always say its a bad idea, my brother would want to know which one of us is going first and I'd want to take look over the cliff.

Analyze each situation independently.

 

[twisted fisher]

lol and i would be the one wondering if the trees at the bottom will slow us enough not to get hurt TOO bad

 

[danger_chicken]

^ I like the way you think

 

[hydrodmg]

i have been pondering this same thoughts for a while on one filter to many tanks and the best idea i came up with is u piped siphoning many tanks in to a single tank that is larger in gallons than the amount of gallons your u pipe is submerged in and filtering the tank that all the siphoned water is in and then the part im stuck on is the return issue. i am sure with valves in a pvc pipe it could be achieved. this would be difficult to do because as your filter does its job you will have a reduced flow of water going in and coming out of the filter but i want to do it personally just to say i did it. but beware of the point of diminishing returns, piratical, unpractical, doesn't matter its your fish room and i know i take a lil pride when i build something for my tanks

 

[danger_chicken]

You might be able to use float valves as a safety for the returns. Something in the way a toilet works.