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Discussion Starter · #1 ·
Okay, so let me premise this by saying I don't want to start an argument, rather a discussion on how aquarium filtration is actually quantified. Coming into this discussion, I am going to assume that you already know the basics of aquatic filtration. If you don't, please read up before commenting.

We often see filters rated for certain sizes of aquariums and we often hear general rules that filters should provide 10x turnover of the tanks total volume. For example, a Rena XP2 is rated for tanks up to 75 gallons with flow rate of up to 300 gph, effectively 4x turnover. In contrast, a Rena XP3 is rated for tanks up to 175 gallons with a flow rate of up to 350 gph, effectively 2x turnover. Surely 50 gph does not provide a stark contrast in filtration capabilities and makes you wonder, why is one filter capable of filtering more than double that of the smaller filter? The only other difference between an XP2 and an XP3 is 2.25" of height. This larger canister, even if marginally, provides extra space for filter media which directly equates to a larger nitrifying bacterial colony.

I'd like to propose a theory and ultimately put down the concept that a high turnover rate equals better filtration. In theory, so long as the water is moving and there is enough filter media, or surface area, for a nitrifying bacterial colony large enough to break down the bio load of the tank, there should be no problem with filtration. Applying this theory, a tank could sustain enough biological filtration using a very low gph flow rate.

There are a few caveats to this theory, such as the notion that the bacteria has more of a chance to 'eat' the toxins in the water with a higher flow rate. There is also the possibility that nitrifying bacteria requires a certain level of flow to sustain itself, I don't know that, I'm kind of blindly making an observation from my experiences.

In no way am I stating that a high turnover rate is bad, but it definitely doesn't do much to increase filtration, at least not biologically. I will concede that the more volume of water that passes through the filter each hour can directly have an impact on mechanical filtration, and chemical filtration as well if you use it. The flow rate could also have a direct impact on oxygen levels in the water as well. I'm not arguing that.

Basically, I hear these 'rules' that are set by the community and I'm not really saying they are bad to follow, but how many of them are actually a must? If I have a 100 gallon tank with the exact same amount of filter media and one has 2x the flow rate of the other, does that actually mean it has 2x the filtration? Wouldn't the bacterial colonies, in theory, be exactly the same?

Thoughts?
 

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I am by no means an expert but with a higher turn over rate I believe it helps with mechanical side of filtration, therefor not allowing all the "gunk" to be left on the bottom of tank and stuck in corner to rot. Would this excess "gunk" cause nitrates to rise higher than it would it were to be picked up by the filter and stored in the pre-filters? Or is this just because of the fact that most cichlids are messy fish and the added turn over rate is there to help keep tank maintenance down?

I know this in no way answers the questions asked in the OP, but thinking maybe there is only a slight increase in flow due to the smaller filters running at the lower end of flow of what is needed to keep the bacteria colony alive and thriving and then the larger ones don't need much more than that to sustain the added bacteria alive in the extra media present with them.

I have been trying to understand this logic myself and this is what I have settled on up to this point. I am also not saying to or not to follow these community set rules but I do see my tank being cleaner with more turnover then without.

Or maybe I have no idea what I am talking about, I dont know. :D
 

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The high turnover rate has nothing to do with how well the bacterial colony performs. So long as the water is flowing enough for it to not become stagnant and kill the colony, it doesn't make any difference what the turnover rate is. The turnover has to do with mechanical and chemical filtration.
Also, I don't view them as rules, moreso as guidelines.
As far as going from 75g to 175g with an XP2 (300gph) and XP3 (350gph), I agree, it seems like a bit of a stretch for a 50gph increase. I too would like to know what they base their numbers on.
 

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could too high a flow force debris through the mechanical media though? the rule of thumb isn't 10x turnover with one filter, its for the whole tank, I will be pretty sure than 1250 gph in one filter would be nearly useless, but 10 filters at 125 gph each probably filter the water extremely well.
 

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I think all the gph figures are with empty canisters. I could be wrong.
I just ran through some popular canisters to calculate turnover using the uppermost aquarium size recommended per filter. I realize turnover certainly isn't everything but found it interesting nonetheless.

205 40, 110gph, 2.75x/hr
305 70, 185gph, 2.64x/hr
405 100, 225gph, 2.25x/hr
FX5 400, 925gph, 2.41x/hr

2211 40, 60gph, 1.5x/hr
2213 66, 116gph, 1.75x/hr
2215 92, 164gph, 1.78x/hr
2217 159, 264gph, 1.66x/hr
2260 396, 635gph, 1.6x/hr

XP1 45g, 250gph, 5.55x/hr
XP2 75g, 300gph, 4x/hr
XP3 175g, 350gph, 2x/hr
XP4 265g, 450gph, 1.7x/hr
 

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I think a discussion on this topic is long over due. I have 3 tanganyika tanks set up and none of them have 10x, If you go by the manufacturers flow ratings, my tanks would average about 6x, but these are usually just pump ratings, not taking into consideration the loss of flow caused by the filter media, so realistically, I probably have 4-5x filtration.

As far as credible information goes, it's hard to find, but here we go.

1. From Dr. Paul Loiselles book, Guide To African Cichlids "To function effectively, all the water in the tank must pass through the filter medium two to three times per hour.(refering to mech. filter.)

" A high flow rate is less important in a biological filter. For this type of filter to be effective, the waste stream must remain in contact with the bacterial flora long enough for the nitrifiers to work on the dissolved metabolites. It is enough if the water in the tank moves through the filter medium once an hour

2 Why not use the manufacturers tank size guidelines? They probably know a little more about filters than we do.
 

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Discussion Starter · #7 ·
GTZ said:
The high turnover rate has nothing to do with how well the bacterial colony performs. So long as the water is flowing enough for it to not become stagnant and kill the colony, it doesn't make any difference what the turnover rate is. The turnover has to do with mechanical and chemical filtration.
This is exactly the point I am trying to make. I also think the same as you do, these gph ratings are undoubtedly done without filter media. I'm not really trying to go into whether these numbers match the mfr claims, more so the concept of flow rate vs filter effectiveness. Theoretically you could have a 6"x6"x6" canister and run 10,000 gph through it, doesn't mean it is an effective biological filter for a 1,000 gallon tank. In contrast, you could have a 6'x6'x6' canister and run 1,000 gph through it and have effective biological filtration for the same size tank.

shellies215 said:
Why not use the manufacturers tank size guidelines? They probably know a little more about filters than we do.
I think that is part of the problem. So many people just believe what they are being told instead of thinking critically about the issue at hand. I for one never believe anything a salesmen tells me, especially when it's their product they are trying to sell me.

Those numbers are interesting GTZ, thanks for the data.
 

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because visibly, one xp3 or 2217, will not keep my 125 clean, I have 2 x 2217 and 1 x xp3 on it and I am still trying to figure it out

also have an xp2, c-220, penguin 350 and ac110, and still not clean. each one of those is rated for a 75 or more except for the c-220. needless to say i'm still trying to figure this one out too
 

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Discussion Starter · #10 ·
shellies215 said:
RRasco, If Fluval was trying to be a salesman, they would tell me I need an fx5 to filter my 40 gallon breeder.
I'm not saying everyone is out to get you, but it's best practice to take the information at hand and formulate your own decision.

From what I hear FX5s are really nice, but you won't catch me spending close to $400 for a canister filter, for any size tank.
 

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My example was a bit exaggerated, but based on my experiance with fluval products, the tank size recommendations on their products seem pretty accurate. For marineland products, I usually go one size bigger than their ratings
 

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RRasco said:
GTZ said:
The high turnover rate has nothing to do with how well the bacterial colony performs. So long as the water is flowing enough for it to not become stagnant and kill the colony, it doesn't make any difference what the turnover rate is. The turnover has to do with mechanical and chemical filtration.
This is exactly the point I am trying to make. I also think the same as you do, these gph ratings are undoubtedly done without filter media. I'm not really trying to go into whether these numbers match the mfr claims, more so the concept of flow rate vs filter effectiveness. Theoretically you could have a 6"x6"x6" canister and run 10,000 gph through it, doesn't mean it is an effective biological filter for a 1,000 gallon tank. In contrast, you could have a 6'x6'x6' canister and run 1,000 gph through it and have effective biological filtration for the same size tank.

shellies215 said:
Why not use the manufacturers tank size guidelines? They probably know a little more about filters than we do.
I think that is part of the problem. So many people just believe what they are being told instead of thinking critically about the issue at hand. I for one never believe anything a salesmen tells me, especially when it's their product they are trying to sell me.

Those numbers are interesting GTZ, thanks for the data.
LOL, and here I thought I was arguing your point :D
Your theory that a higher turnover rate doesn't equal better filtration is valid, to a point. That point being where the filter doesn't provide adequate mechanical and/or chemical filtration for the volume of water in the tank.
 

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It is my belief that canister manufacturers base their performance stats on biolgical filtration. And they are extremely well at bio filtration. Where they lack is in mechanical, you get to a point where you just liquify the detritus collected.

ROT for filtration is 2-3x's for bio and for many that has proven to be true. But there are exceptions with certain stock and tank sizes.

If your concern is for 0,0,<20 ammonia,trItes and trAtes than most cans @ 3x's turnover will be just fine.

For mech it really depends on tank size and 'scaping. 5x's turnover starts to show results and helps with dead spots but the more turnover and better media will really show in clarity. I shoot for the floating in air look and pay more attention on mech filtration than bio as bio pretty much takes care of itself. 10x's is not uncommon on prolly half our tanks and from five feet or so distance you could pick out those tanks with ease from the water collumn alone.

Whatever works for you is the best combination and that can only be found through trial, error and quite a few water tests.
 

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fox said:
For mech it really depends on tank size and 'scaping. 5x's turnover starts to show results and helps with dead spots but the more turnover and better media will really show in clarity. I shoot for the floating in air look and pay more attention on mech filtration than bio as bio pretty much takes care of itself. 10x's is not uncommon on prolly half our tanks and from five feet or so distance you could pick out those tanks with ease from the water collumn alone.

Whatever works for you is the best combination and that can only be found through trial, error and quite a few water tests.
I completely agree. I had a 120 gallon with two 12" Oscars and several African Cichlids running for several months with just a penguin filter without any media in it. It was just for water flow. The nitrogen cycle held up fine! The tank was in need of some mechanical filtration though. I believe that for a well established tank, the surfaces inside the tank can provide enough biological filtration. All I worry about is mechanical and chemical filtering. I take the manufacturer's recommendations, and the general rules with a grain of salt...
 

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I think the first misconception that needs to be cleared up is that Volume of tank divided by the flowrate of the filter = turnover rate. This is not true.

Turnover rate can be calculated by T= 9.2(V/f) Where T= the number of hours it takes to run 99.99% of the water through the filter one time, 9.2 is the purity coefficient, V= the volume of the aquarium, and f= the flow rate. This is because we are mixing the filtered and unfiltered water in the same container (the aquarium). Some of that water that just exited the filter is going to go right back in again while other water is going to stay longer in the aquarium before going through the filter. This equation allows you to account for that.

A 75 gallon aquarium with a 300 gph pump would take 2.3 hours to filter the water one time. A 175 gallon aquarium with a 350 gph pump would take 4.6 hours to do the same.

In a pond filtration system one turnover per day is generally the rule of thumb. In an aquarium, (which has a much higher stocking density) the turnover rate should be more frequent. However there are too many variables in the filtration system to calculate what this magic number should be for any given volume.

In mechanical and chemical filtration applications the more turnovers per day the more efficient the filter will be at clearing the water.

In a biological function the slower the water the more contact it has with the biological filter bed for removal of ammonia and nitrite. However if the flow is too slow through the column the available oxygen could be stripped out and you lose efficiency.

In either case, at 4.6 hours for a turnover that is still 5 times a day which is pretty respectable for a biological filter although it is on the short side for mechanical and chemical filtration possibly.

Andy
 

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Perhaps we should consider the possibility that not all the water in the tank will pass through the filter even once per hour, regardless of flow rates and turnover. It may be similar to water changes, in that if you change 50% today, 50% tomorrow, and 50% the next day, you still haven't changed 100% of the water. Perhaps it also doesn't matter. I don't know how you would determine the actual amount of the water that actually passed through the filter, and if it all did. In addition, we know that low flow filters such as air driven sponge filters work to keep a tank healthy. It is what filters most of my tanks. My two cannisters sit idle.
It seems from most of the posts I have seen, people want their filters to remove visible particles and detritus from the water, equating a crystal clear tank with a healthy one. If all that solid material is being hidden in a cannister, it is still in the tank.
Assuming a regular water change regimen, the removal of detritus from the tank, rather than letting it accumulate in a filter is probably a better solution. For sure, nitrate numbers will rise more slowly. It always makes me laugh when I hear UGFs called nitrate factories; every working filter is a nitrate factory. What affects the nitrate level of a tank is the bioload, not the type or brand of filter.
I guess what we need to differentiate is between "clearing" the water and "cleaning". Polished water is great to look at, and if you have used a diatom filter to remove material from the tank, this is different than removing it from the tank and hiding it in a filter. This would be a situation where clear and clean would by synonymous. However, I don't think a tank needs to be crystal clear to be healthy.
 

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Mech filtration is more than just sweeping it under the rug so noone see the mess. Well at least for me it is.

I am gung ho on mech filtration and have expressed this before. What needs be done is to remove the socks/ pads/ floss/ sponge once or twice a week for a good rinsing or replacement. On our tanks the socks do not go more than three days and the sponges get squeezed at the least with every WC. We also keep HOB's on most of our smaller tanks and fill em with floss which gets discarded with each WC. So I guess with us clean water starts with clear water and I shoot for clear water.

Cans ... I use em just for bio, too much a hasstle to use one for mech as I go three months or so 'tween maintenance to prolong the orings and other gremlins that pop up when they get opened.

YMMV
 

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Great thread, a topic I have recently struggled with. I am currently designing a sump for an upgrade from a 90 to a 135-150 gallon tank and trying to determine what turnover I think is best. I'm finding it difficult. I agree that the flow rate of a canister is less when media is present. My question is this: the return pump is pumping water from a sump chamber holding only water, after it has passed through the media chambers. Would this be considered full flow (of course taking into consideration how high the return water is being pushed) based on the head charts for the pump?

And for each filter, whether it be HOB or canister would the flow rate not vary based not only on the type of filter media being used, but also how long the media has been in the filter (ie. how much trapped gunk it has, therefor impeding water flow)?
 

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A wet/dry filter would not be affected by clogged media. Water will simply bypass around it and make it's way to the pump by any means necessary. Other than the effects of gravity (head pressure) and friction in the plumbing lines the flow would be the full force of the pump.

For HOB filters they also have bypass arrangements. Water will simply flow around the media and back into the tank. So clogged media will affect the "effective" water flow (water through the media) but not the net water flow. A clogged strainer or intake will have a strong effect on water flow however. The same also applies to canister filters.

In canister filters the media is located upstream of the pump and essentially acts like a large strainer. When it becomes clogged the water flow will be affected. How quickily it clogs will depend on the type and coarseness of the media as well as how much debris is generated by the aquarium.

Andy
 

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Great thread as I am trying to figure out if my Eheims will filter my new tank sufficiently or if I have to add a 3rd canister. I am not a fan of HOBs though I do have one at the ready if needed.
 
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