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Discussion Starter · #1 ·
Hi all,

I'm gearing up for my first-ever planted tank, but still undecided on what size I want. It'll probably either be a 5g or 20g, just comes down to how much room I want to have available. I'm thinking my eventual tank will be have a solid carpet and one or two tall plants, and a scattering of enough fish to keep from looking too static.

When I went to my local fish store (small business, not chain), the guy there, Garret, recommended a 100 gpm filter for the 5.5 gal tank he had available! He said that's the setup he used in his own nano, and it allowed him to crowd in fish and plants without a care in the world.

So my question is this: Is that not a ridiculous flowrate for such a small tank? If my filter is recirculating the tank's entire volume ~20 times an hour, will the current not be significant if I want to keep a betta or some guppies? I thought that a filter which with a flowrate twice your tank volume per hour was high enough.
 

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There are a couple different things to consider:

1. In general you want 10x turnover per hour on a smaller tank. This corresponds to decent flow, but nothing crazy. Larger tanks sometimes only use 2-5x per hour due to the pure volume of water they are moving. 20x is on the high side, but not totally crazy, but that leads to point 2. If you are only keeping a betta in the tank then you can go for lower flow. They have been bred over hundreds of generations to sit in tiny bowls and can no longer stand up to current. They also breathe air so they don't need nearly as much surface agitation to keep oxygen levels up.

2. Flow ratings on filters are measured when they are empty. If your filter is rated for 100 gph then that is with no filter media in it. With a sponge, bio media, and fine filter media in there your flow will be closer to 40-50 gph. This means your 20x turnover suddenly becomes 8-10x turnover in your actual setup.

So in summary, if you are keeping guppies or other small water breathing fish then 10x per hour is what you should shoot for, and the filter that was recommended should be fine. If you plan on just keeping a betta than I would suggest downsizing so he isn't blown all over the place.
 

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When I went to my local fish store (small business, not chain), the guy there, Garret, recommended a 100 gpm filter for the 5.5 gal tank he had available! He said that's the setup he used in his own nano, and it allowed him to crowd in fish and plants without a care in the world.
Stop taking advice from Garret (or from anyone else who is talking to you with an eye on profits!). You could flow 1 billion times the volume of water per hour and it still doesn't allow you to overstock your tank. The amount of flow has nothing to do with the biological capabilities of a filter.

However, that doesn't mean a larger filter is a bad idea. You are correct to be concerned about how strong of a current your filter might produce but there are some ways to slow that down if you eventually find yourself in that position.
 

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This is a question with lots of answers and you may not be able to say at this time. You can buy big and if it is too strong simply restrict the flow. Lots of things do that. A simple sponge over the intake tube can cut it. But then since larger filters are often more expensive, it can become an economics question. If you don't need the bigger filter but will in a few months as you will move to a larger tank, it can make sense to buy larger now and not replace. But if the filter is never going on a larger tank, it can be money saved now as well as not waste the effort to cut flow.
What is in the tank will matter a whole bunch, too. You don't want suck all the fry up the pipe, if that comes around.
How well do we predict the future?
I go smaller and wait to see the need, then add more.
 

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From my experience one tank always leads to bigger one, then that tank leads to a bigger one, and so on. I always get a filter that is a little more than I need. Sometimes I find the manufacturer suggestions on tank size for filters are a little exaggerated, so this covers you. Depending on how you pack a canister, or how dirty it is greatly effects flow. I'm pretty sure manufacturer flow rates are on a brand new, lightly packed filter. Where they should be on a average flow rate of an in use filter with some gunk in it. Just my opinion.
 

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A larger filter likely also holds more water, so more total volume of water could mean able to add more fish in a small tank. So a larger filter really can allow you to "overstock". A larger filter also would have more biological capabilities, as it can hold much more media.

+1 to what aja31 said.

I have never heard anyone ever say, "Man, I wish I didn't have so much filtration!"
 

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A larger filter likely also holds more water, so more total volume of water could mean able to add more fish in a small tank. So a larger filter really can allow you to "overstock". A larger filter also would have more biological capabilities, as it can hold much more media.

+1 to what aja31 said.

I have never heard anyone ever say, "Man, I wish I didn't have so much filtration!"
You might be stretching the truth to fit a want there. Unless you're adding a sump with significant volume this just really isn't too practical. If I put a 100 gallon sump on a 5 gallon tank could I keep a bunch of koi in the 5 gallon display?
 

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If you want a decent number of fish, get at least a 20 LONG. The bigger footprint is much more useful than the height when it come to heavy stocking imo.

I would be more concerned with amount of bio material a filter can hold rather than flow rate. You could always supplement flow rate with powerhead.
 

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Discussion Starter · #11 ·
If you want a decent number of fish, get at least a 20 LONG. The bigger footprint is much more useful than the height when it come to heavy stocking imo.

I would be more concerned with amount of bio material a filter can hold rather than flow rate. You could always supplement flow rate with powerhead.
20 long is definitely what I'm looking at right now, and I'll go ahead and stick with the 100 gph filter, since I expect someday in the future I'll upgrade tank size and might as well be ready.

Thanks for the opinions everyone!
 

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20 long is definitely what I'm looking at right now, and I'll go ahead and stick with the 100 gph filter, since I expect someday in the future I'll upgrade tank size and might as well be ready.

Thanks for the opinions everyone!
If you are planting that tank, then the 100 gph won't be sufficient. You will have to add powerhead later to get decent circulation. Keep that in mind when you are planting and leave room/path for powerhead.
 

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Discussion Starter · #15 ·
If you are planting that tank, then the 100 gph won't be sufficient. You will have to add powerhead later to get decent circulation. Keep that in mind when you are planting and leave room/path for powerhead.
I am planning to plant and have fish, but what you just said seems contrary to what everyone else has been telling me. Why won't 100gph be enough?

As to the circulation, I was pondering if there were ways to plumb my filter's intake over to the far side of the tank (with PVC, perhaps) to get a greater distance between the filter supply & return and induce more current. I'll have to poke around the DIY forum and see what they say.
 

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I am planning to plant and have fish, but what you just said seems contrary to what everyone else has been telling me. Why won't 100gph be enough?

As to the circulation, I was pondering if there were ways to plumb my filter's intake over to the far side of the tank (with PVC, perhaps) to get a greater distance between the filter supply & return and induce more current. I'll have to poke around the DIY forum and see what they say.
Long tank is a different beast than the rest. If you are going to have any sort of hardscape (rock, wood) in the middle, your 100 gph flow will almost guarantee won't reach the other end of the tank. I have a 22g long which is slightly longer than standard 20long and I'm using a 150gph cannister + 240gph koralia to get sufficient flow in the tank. The cannister flow rate will considerably decrease as the media and pipe get dirty.
 
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