Tank turnover theories

I’ve noticed when reading articles and care sheets about different types of fish, and also on Internet forums people often mention minimum times you should turn over the tank volume, often ridiculously high ratios like 10 times the tank volume are quoted, to me it seems without any workings or science to back this up.

While I agree with the general consensus that more filtration is never a bad thing (unless you have fish that struggle to swim in a lot of movement) but I’m interested as to why a certain flow rate would be needed in an aquarium? If your filter has enough media to handle the bio load, and you have sufficient aeration/movement, I struggle to see why anyone would strive to achieve 300 gallons of flow an hour in say a 30 gallon tank, or even 5 times the volume. Seems a bit like the inch per gallon rule to me, something people quote without really knowing too much about it. I can see why in heavily planted tanks it’s more important, but African cichlid keepers seem to think it’s very important and they don’t have plants.

I’d like to know people’s thoughts and theories on this, as it’s something I completely overlook, after all my mechanical filtration, bio media and pipes, my canister filter only has an actual output of about 40% of the manufactures quoted flow, which is about 2.5 times the tank volume, but as far as I can tell it still easily handles (no ammonia or nitrite) the bio load in quite heavily stocked tank.

 

I encourage anyone to join a club and visit other peoples set up’s. Even if it’s just on zoom ( virtually) at the moment.

There are no fish keeping clubs in my state. The closest one is 2 states and 4 hours away in Boston

Does anyone know of online clubs that can be joined?

 

FishDin Try searching aquarium Society in your state?

An old fashioned name but that’s the English language for you.

Within my main club I have found three other groups that meet regularly but have NO official on line or hard copy newsletter. Without being in the first group I would not know of a “ plant group “ a killifish group “ and a “ girls only group “ that all fly under the radar and have members that are not currently members of the main official club/ aquarium society.

 

Very nice, I’m still confused though about the claims of 10X plus in GPH. I’ve tried many different filters, and I’ve never tested a canister filter when hoses are connected and filled with media that has an actual output above 50% of what it says on the box. So if the manufacturer claims the pump has a flow rate of 1000 GPH, it’s much more like 500 GPH when set up on a tank, or if they say 500 GPH it’s more like 250 GPH.

So unless I’ve just had bad luck with canister filters, say if I had a 50G tank, to realistically turn the tank over 10x per hour I’d need 2 FX6 filters (563 GPH manufacturers claim) to make sure I turned the tank over 10 times. That still seems obscene to me on a 50-60 gallon tank, unless the tank was stupidly over stocked.

The things you see printed on the box containing the filter were probably put there by the marketing department, not the engineers who designed the filter. Their job of the marketers is to get people to purchase their filters. Thus, they talk about all the great features of the filter. The flow rates shown are likely to be measured under "best case" conditions. That means the filter is new, the water is clear, and there is no filter media in the filter. That is as good as it gets. As soon as you fill the filter with media and the intake tube, pump casing and impeller start to develop a biofilm, the water flow rate will drop by 50% or more.

Likewise, when a specific filter size is recommended by the marketing department for a specific size tank, once again it is likely to be under best case conditions. If your tank is heavily planted, understocked and underfeda, the stated sizes will be adequate. They is why they state that the filter is suitable for tanks up to a certain size. The "up to" value works if you have a "best case" scenario.

Based on my own personal experience over decades of fishkeeping, I have found that the stated tank sizes on the filter boxes are overly optimistic. If you purchase a filter in which the stated flow rate on the size of the filter box is approximately 10 X the tank size, the filter will function under typical tank conditions. Thus, for a 55 gallon tank, one of the filters I recommend is the Aquaclear 110 which is supposed to be suitable for tanks up to 110 gallons (under ideal conditions). However, with a rated flow of 500 gph, it is more suitable for a 55 gallon tank holding 50 gallons of water. While the filter will fit on the rim of a 110 gallon tank, you are likely to find that two such filters are needed to provide clear water in a tank of that size.

 

The things you see printed on the box containing the filter were probably put there by the marketing department, not the engineers who designed the filter. Their job of the marketers is to get people to purchase their filters. Thus, they talk about all the great features of the filter. The flow rates shown are likely to be measured under "best case" conditions. That means the filter is new, the water is clear, and there is no filter media in the filter. That is as good as it gets. As soon as you fill the filter with media and the intake tube, pump casing and impeller start to develop a biofilm, the water flow rate will drop by 50% or more.

Likewise, when a specific filter size is recommended by the marketing department for a specific size tank, once again it is likely to be under best case conditions. If your tank is heavily planted, understocked and underfeda, the stated sizes will be adequate. They is why they state that the filter is suitable for tanks up to a certain size. The "up to" value works if you have a "best case" scenario.

Based on my own personal experience over decades of fishkeeping, I have found that the stated tank sizes on the filter boxes are overly optimistic. If you purchase a filter in which the stated flow rate on the size of the filter box is approximately 10 X the tank size, the filter will function under typical tank conditions. Thus, for a 55 gallon tank, one of the filters I recommend is the Aquaclear 110 which is supposed to be suitable for tanks up to 110 gallons (under ideal conditions). However, with a rated flow of 500 gph, it is more suitable for a 55 gallon tank holding 50 gallons of water. While the filter will fit on the rim of a 110 gallon tank, you are likely to find that two such filters are needed to provide clear water in a tank of that size.

To be honest this is what I suspected when I started the thread, when people state that you should or they themselves turn over their tank volume 10X per hour, what it actually means is a safe rule of thumb is to buy a filter with a pump that in theory could turn over the tank 10 times in lab conditions, which in reality will be much less, likely half. That makes much more sense, I couldn’t find a logic in home aquarium keepers actually striving to ensure they turn their tank volume over 10 times in real terms.

 

FishDin Try searching aquarium Society in your state?

An old fashioned name but that’s the English language for you.

Good call. I did find an aquarium "Society" in my state.

Unfortunately they are 2 1/2 hours away on back roads and they haven't been active for a year.

The reality of living in a sparsely populated place... It makes even more thankful for forums like Fishlore.

 

I’ve noticed when reading articles and care sheets about different types of fish, and also on Internet forums people often mention minimum times you should turn over the tank volume, often ridiculously high ratios like 10 times the tank volume are quoted, to me it seems without any workings or science to back this up.

While I agree with the general consensus that more filtration is never a bad thing (unless you have fish that struggle to swim in a lot of movement) but I’m interested as to why a certain flow rate would be needed in an aquarium? If your filter has enough media to handle the bio load, and you have sufficient aeration/movement, I struggle to see why anyone would strive to achieve 300 gallons of flow an hour in say a 30 gallon tank, or even 5 times the volume. Seems a bit like the inch per gallon rule to me, something people quote without really knowing too much about it. I can see why in heavily planted tanks it’s more important, but African cichlid keepers seem to think it’s very important and they don’t have plants.

I’d like to know people’s thoughts and theories on this, as it’s something I completely overlook, after all my mechanical filtration, bio media and pipes, my canister filter only has an actual output of about 40% of the manufactures quoted flow, which is about 2.5 times the tank volume, but as far as I can tell it still easily handles (no ammonia or nitrite) the bio load in quite heavily stocked tank.

my idea is because if a fish dies and your asleep there is enough beneficial bacteria processing it efficiently so when you wake up hopefully there not dead but honestly idk I think it's a rumor a company started then everyone started saying it cause if you want flow, you could always get a wave maker also think of rivers constantly filtering and it never coming back to the same point

 

I am one who recommends purchasing filters rated for 10X the tank volume. However, that does not mean that the turnover rate will be 10X the tank volume. The filter rating is the maximum flow that will occur with no filter media to impede flow. By the time you add a prefilter sponge, which I highly recommend, and filter media, the flow rate is likely to drop to half of the rated flow, perhaps less. As the prefilter and filter media start to clog with debris, the flow will slow to a trickle.

I have a 55 gallon tank in which I run a Aquaclear 110 rated at 500 gph and a Aqueon 75 rated at 400 gph. That is an overall flow rate of 900 gph which is 16X the tank volume. However, with prefilter sponges and a full complement of filter media, the flow is not excessive.

If I used a single Aquaclear 50 filter in the tank (200 gph), the flow would not be nearly sufficient for the tank. Aquaclear recommends the filter for tanks UP TO 50 gallons, but it is really more suitable for a 20 gallon tank. I have used such filters in a 20 gallaon. Even the Aquaclear 70 (300 gph) is not quite big enough for a 55 gallon tank, but it works fine in a 29 gallon tank. I do have a AC 70 in a 40 gallon breeder, but that is to supplement a canister filter, not as the sole filter.

 

I have a 50 gal tank with an old Rena Filstar XP2. To the company's credit, they list flow rates with and without filter media. The filter media is 2 sponges; one course and one medium. This is from the filter description:

API Filstar M (XP2) Series Canister Power Filters

• Free Technical Support From Rena OEM Sales
• Flow: 300 U.S. GPH (1150 L/H)
• Suitable for Aquariums up to 75 U.S. Gallons (280 L/H)
• Canister Volume: 1.4 U.S. Gallons (4.4 L)
• Flow w/media: 160 U.S. GPH (605 L/H)

So with just 2 thin sponges the flow is cut almost in half.

 

I have a 50 gal tank with an old Rena Filstar XP2. To the company's credit, they list flow rates with and without filter media. The filter media is 2 sponges; one course and one medium. This is from the filter description:

API Filstar M (XP2) Series Canister Power Filters

• Free Technical Support From Rena OEM Sales
• Flow: 300 U.S. GPH (1150 L/H)
• Suitable for Aquariums up to 75 U.S. Gallons (280 L/H)
• Canister Volume: 1.4 U.S. Gallons (4.4 L)
• Flow w/media: 160 U.S. GPH (605 L/H)

So with just 2 thin sponges the flow is cut almost in half.

Exactly, that is with just two thin sponges. If you pack your HOB with media, the decrease in flow will be even greater.

I would never recommend that Filstar filter for a 75 gal tank. If your 50 gal tank is lightly stocked and lightly fed, it might work just fine.

 

It's been running on that tank for 11 years. There are about 30 adult Julidochromis and a pair of compressiceps in there as well as 6-8 nerites. I feed once a day, but not lightly. I clean the filter 2-3 times a year.