# Using a big filter on a small tank?



## pitabread

I was wondering if anyone has tried using an extra large filter for a much smaller tank than recommended for.

The reason is, I want to set up a 5.5 gallon nano. I figure that using an extra large HOB filter will give me extra water volume. I calculated that I would get about an extra 1/2 gallon using an Aquaclear 70 versus an Aquaclear 20.

I realize that the larger filters are probably too strong, but could I either replace the motor with an underpowered one, or block the flow to reduce water current?

*edited to add:* In looking at the Aquaclear manual, I notice they all use the same motor, but different impellers. Would it possible to simply put in a smaller impeller and get a lower flow rate?


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## lildark185

*edited to add:* In looking at the Aquaclear manual, I notice they all use the same motor, but different impellers. Would it possible to simply put in a smaller impeller and get a lower flow rate?[/QUOTE]

I think the point of having a bigger filter is to have stronger flow of water and faster turnover of water. If you put in a smaller impeller (assuming that you could get it to work) the larger volume that u would get from the larger filter would take longer to fill up with the smaller impeller. Then by the time it does fill up, wouldn't the water flow from this slower uptake of water reduce the filter to a trickle and not a nice stream? Thats just what I'm thinking, but might not be true.


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## Chris S

That amount of flow would be like a fast flowing stream.Maybe that is what you are going for? The impellers are probably not interchangeable because of the size of the drive shaft.but worth looking at i guess to see for yourself./


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## pitabread

I don't want too much flow, but I do want the extra water volume if I can get it.

I looked up the impeller parts on the Hagen web site. The impellers for the Aquaclear 20, 30, 50 and 70 all look exactly the same except for the size of the blades. I imagine they would be interchangable, since the motors are identical on those filters. Only the Aquaclear 110 has a different motor and a bigger impeller from the looks of things.

I have an Aquaclear 20 right now, so I could test its impeller in a 70 and see how it works. If it's not good enough, I could buy the impeller from the 30 or 50.


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## Moo

why not just try a supersmall canister?


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## pitabread

*Moo*, I'm looking to put a submersible heater in it, and possibly CO2 diffusion as well. An HOB filter is the best (and cheapest) solution for that.


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## werner

I have an AC mini (20) running on my 5.5gal betta tank. It had too much water movement for me so I shaved off part of the impeller blades.

All of the smaller AC filters (mini/20, 150/30, 200/50, 300/70) use the same motor housing, but the impellers just have larger/more blades as the sizes get bigger.

An AC 70/300 seems way too big to put on a 5.5 gal- it's almost as big as the tank itself. However... I just happen to have a spare one sitting in my box o' fish stuff, so I'll go play with it to see what it will do on a small tank (got a spare one of those too.) I also have an extra AC 200/50 that I can try out. I'll post the resuls when I'm done messing around with them.


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## Moo

ah alright. I see your point. Lol. Yeah thats prolly the best.


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## werner

I tried out some different impeller/filter combinations and here are my results:

The 70/300 filter has a much bigger intake tube than the smaller versions, and has a very hard time priming itself when there's a smaller impeller in there. It did work with the impeller from the 50/200, but that was still too much current for a small tank.

The 50/200 filter would be a better choice since it has the same intake size as the 20/mini. If you put the 20/mini impeller in it, you would basically have a 20/mini filter with a greater media/water volume.

Hope that helps!


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## werner

I just figured out that you're wanting to do this in order to put a heater in the filter. Where do you plan to put it? Once the media's in the filter, there's no room for it.


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## pitabread

Thanks for the testing *werner*. I guess you didn't have an AQ 30 impeller, though? I figured I'd get the 70 and the 30's impeller and try that combo. Good to know the 70 and 20's impeller wasn't really viable.

As far as media goes, I wasn't going to put much in. I was probably going to stick a strip of sponge across the filter output, and maybe stick a few bioballs as well for bacteria. I wasn't planning on using carbon. Again, my main purpose for the filter is extra water volume and a place to put the equipment.

Maybe I'll just get a 30, 50 and 70, and mix 'n match pieces until I find an optimal solution. Then I'll just return whichever filter I don't use.

*edited to add:* Btw, is it possible to use the smaller intake tube from the 50 on the 70?


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## mrbelvedere138

Maybe an Eheim 2213? Not very expensive......


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## werner

I'd suggest staying away from the 70 altogether. It had a hard enough time priming itself with the 50 impeller, so I don't think it could do it at all with the 30 impeller. Even with a smaller impeller, there was still way too much flow for a little tank (increased CO2 outgassing.) Besides, if you're trying to minimize equipment in your tank, you won't like the huge intake tube (not interchangeable with the smaller ones.)

If your heater fits, I say go with the 50 filter with a 20 impeller. Or just remove 2 of the 4 fins from the 50 impeller (cheaper). 

'Course I would be hesitant to put a heater in a filter at all (blah, blah, same reasons as stated in your other thread...)


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## pitabread

Doh, I should have read your latest post sooner. As it is, I placed an order for the AQ 70 last night (and an AQ 30 that I'll be using on a 20 gallon).

At any rate, even if the 70 doesn't work out, I may regulate it to duty on my 56 gallon reef tank. I'll be needing something on there to run carbon when I start stocking corals in a couple months. I'm sure the 70 would be ideal for that.


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## pitabread

Got my AQ 70 (and 30) today. *werner*, I can see what you mean about the intake tube on the 70. It's freakin' huge! I'm guessing that the priming issues you were having were probably because the wider intake required greater water pressure to get going. Therefore, I have a plan to mod it...

I've got some flexible plastic tubing, with a much narrower diameter. I plan to put the tubing through the intake tube. I'll block off the surrounding gap on the intake tube, so the water should only be going through the flexible tubing. I'm also going to try to figure out a way to attach a smaller extension tube, too. Hopefully this way, less water pressure will be required to prime the filter and it will be able to function with a smaller impeller.

I'll post how it goes in a couple of days...


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