Water flow and water line.

Dave125g

Member
I wanted to talk about how your water level affects your filtration with an HOB. With the water line above the filter output your filter operates much more efficiently. It's also quieter. By contrast, with the water line below the filter output your filter is basically filtering water that was just filtered. Leaving 3/4 of the tank water unfiltered. For those who say I need the oxygenation, I say get an airstone. For those who say "I like the waterfall sound", I say buy a waterfall decoration. So, for the health of you aquarium fill your tank.
 

MomeWrath

Member
YASSSSS!! Visible waterlines make me crazy too.
 

mattgirl

Member
Magicpenny75 said:
YASSSSS!! Visible waterlines make me crazy too.
Me too !!!! my 55 is about 1/4 inch lower on the right side so I have to live with a tiny water line. I have learned to live with it but wish it weren't so :( But I always keep my tanks filled high enough to keep the HOB's output below the water line.
 
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Dave125g

Member
Yes I don't like to see the water like. It's an eyesore. It looks like your too lazy to top off your tank. But more then that it's not healthy for your tank.

mattgirl said:
Me too !!!! my 55 is about 1/4 inch lower on the right side so I have to live with a tiny water line. I have learned to live with it but wish it weren't so :( But I always keep my tanks filled high enough to keep the HOB's output below the water line.
It's tough to level the stand. As accurate as you get it, it changes when you fill the tank.
 

mattgirl

Member
Dave125g said:
It's tough to level the stand. As accurate as you get it, it changes when you fill the tank.
Right. when hubby set this one up for me he got it as level as possible. He is a perfectionist so got it perfect but once filled it changed :( Fortunately the stand is perfectly flat so the tank is well supported. The 1/4 inch difference should never cause a problem other than a small eyesore.
 

Cichlidude

Member
Of course if you place your HOB between the 1/3 and 2/3rds mark in your tank it will do much better than at the left or right side.
 
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Dave125g

Member
Cichlidude said:
Of course if you place your HOB between the 1/3 and 2/3rds mark in your tank it will do much better than at the left or right side.
Yes mine always go in the middle. I didn't think about that in my drawing. Thanks for pointing that out.
Although that's not the point I was trying to make.
 

ForceTen

Member
mattgirl said:
Me too !!!! my 55 is about 1/4 inch lower on the right side so I have to live with a tiny water line. I have learned to live with it but wish it weren't so :( But I always keep my tanks filled high enough to keep the HOB's output below the water line.
Have you considered leveling it? I am OCD about stuff like this and would be hard pressed for a good nights sleep with a tank that's not level.

You could do a major water change. Take out any heavy objects and be able to easily level the aquarium.
My wife has these sliders that go under furniture so they can be moved around easily. With the sliders came a lifting tool. Its designed to lift the furniture to put a slider under.
Its perfect for this and a 55 gallon with not to many heavy rocks could be leveled by one person. Two people are much better.
 

Cichlidude

Member
Dave125g said:
Yes I don't like to see the water like. It's an eyesore. It looks like your too lazy to top off your tank. But more then that it's not healthy for your tank.
Well what folks can do is fill the tank to where you want it. Then simply grab some black electrical tape and go around the outside to mark the level just below what you want. Now when the water level drops a bit... it looks perfectly level.
 
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Dave125g

Member
ForceTen said:
Have you considered leveling it? I am OCD about stuff like this and would be hard pressed for a good nights sleep with a tank that's not level.

You could do a major water change. Take out any heavy objects and be able to easily level the aquarium.
My wife has these sliders that go under furniture so they can be moved around easily. With the sliders came a lifting tool. Its designed to lift the furniture to put a slider under.
Its perfect for this and a 55 gallon with not to many heavy rocks could be leveled by one person. Two people are much better.
Water weighs about 10 pounds per gallon add that to the weight of the substrate, tank and stand. What your suggesting is near impossible and very dangerous. Only safe way is to remove every thing, sure up the low corner and refill. If your lucky it only needs to be done once.


We're starting to get off topic. I created this thread to explain the relationship between water level and filter performance.

Cichlidude said:
Well what folks can do is fill the tank to where you want it. Then simply grab some black electrical tape and go around the outside to mark the level just below what you want. Now when the water level drops a bit... it looks perfectly level.
Yes but I just top it off. Seems a bit easier.
 

ForceTen

Member
Dave125g said:
Water weighs about 10 pounds per gallon add that to the weight of the substrate, tank and stand. What your suggesting is near impossible and very dangerous. Only safe way is to remove every thing, sure up the low corner and refill. If your lucky it only needs to be done once.
We're starting to get off topic. I created this thread to explain the relationship between water level and filter performance.
I thought water was 8Lbs per gallon? Minor leveling adjustments are indeed possible and I am doing it right now.
I have 100Lbs of sand and three inches of water in my new 40 gallon tank. I am leveling it with weight in it because its more accurate and more reliable. Lush carpet with thick padding is the issue for me. A hard floor makes this job easier, but leveling a tank on carpet is not as easy as some may think.
While leveling with nothing in the tank is the best bet, its not always possible and in many cases its not good enough
 

Momgoose56

Member
Dave125g said:
I wanted to talk about how your water level affects your filtration with an HOB. With the water line above the filter output your filter operates much more efficiently. It's also quieter. By contrast, with the water line below the filter output your filter is basically filtering water that was just filtered. Leaving 3/4 of the tank water unfiltered. For those who say I need the oxygenation, I say get an airstone. For those who say "I like the waterfall sound", I say buy a waterfall decoration. So, for the health of you aquarium fill your tank.
Okay! Interesting! I have to say, I don't care to hear my filter splashing but as your incredibly steady handed depiction shows, the 'waterfall effect' also creates additional surface turbulence and increased water oxygenation. Plus, have you tested your water flow theory with some sort of semi-buoyant small object that will actually follow the flow of water from the outlet? What I would recommend is that people adjust the level od water in their tank with a HOB filter, to the particular needs of the tank.
What I think actually happens, knowing some fluid mechanics, is that the resistance of the surface water to water falling on it would spread the flow out more at the surface level as opposed to water, entering water without that resistance which I think, would slow and spread out further down (maybe halfway) in the tank. Water is a great cushion. That's why ballistics testing involves shooting bullets from above into a tank of water. Any bullet will come to a dead standstill within a few feet of the surface. A more dramatic example of how resistant water is: If you jump from a 30 foot cliff and land in the water flat on your rear end, you're not only going to have bruising on your rear and posterior thighs, but you might have shock/impact injury all the way up your lower spine. Just my educated ruminations...what do you think?
 
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Dave125g

Member
ForceTen said:
I thought water was 8Lbs per gallon? Minor leveling adjustments are indeed possible and I am doing it right now.
I have 100Lbs of sand and three inches of water in my new 40 gallon tank. I am leveling it with weight in it because its more accurate and more reliable. Lush carpet with thick padding is the issue for me. A hard floor makes this job easier, but leveling a tank on carpet is not as easy as some may think.
While leveling with nothing in the tank is the best bet, its not always possible and in many cases its not good enough
Yes 8.2 pounds per gallon. I use 10 because it's easier to multiple. Moving a tank with water in it can cause seals to fail. You can level your tank with water if you want. But I would rather not have 125 gallons of water flooding my living room.

Again this is off topic.
Momgoose56 said:
Okay! Interesting! I have to say, I don't care to hear my filter splashing but as your incredibly steady handed depiction shows, the 'waterfall effect' also creates additional surface turbulence and increased water oxygenation. Plus, have you tested your water flow theory with some sort of semi-buoyant small object that will actually follow the flow of water from the outlet? What I would recommend is that people adjust the level od water in their tank with a HOB filter, to the particular needs of the tank.
What I think actually happens, knowing some fluid mechanics, is that the resistance of the surface water to water falling on it would spread the flow out more at the surface level as opposed to water, entering water without that resistance which I think, would slow and spread out further down (maybe halfway) in the tank. Water is a great cushion. That's why ballistics testing involves shooting bullets from above into a tank of water. Any bullet will come to a dead standstill within a few feet of the surface. A more dramatic example of how resistant water is: If you jump from a 30 foot cliff and land in the water flat on your rear end, you're not only going to have bruising on your rear and posterior thighs, but you might have shock/impact injury all the way up your lower spine. Just my educated ruminations...what do you think?
On topic. Thanks for the ballistics lesson, and the complement. I do think your comparing apples to oranges though.

I addressed oxygenation in the first post. In addition to an airstone....live plants are really all you need. But if your not into that, an output below the water line provides enough surface agitation. If not I'd say your under filtered.

As far as a test. Not exactly. I'm not a scientist so I haven't used a proper scientific method. However I keep Italian vals. I have observed there movement with the water line both above and again below the filter output. That's how I came to my conclusion. You may call it a hypothesis if you wish.
 

Cichlidude

Member
You have to consider the HOB also. Almost all HOBs with the exception of the Tidal filters have a sharp drop off. The Seachem Tidal filters have an extended outflow to push the water across the tank instead of dropping it straight down into the tank.
 
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Dave125g

Member
Cichlidude said:
You have to consider the HOB also. Almost all HOBs with the exception of the Tidal filters have a sharp drop off. The Seachem Tidal filters have an extended outflow to push the water across the tank instead of dropping it straight down into the tank.
I didn't consider cheap HOBs. The aqueon HOBs don't have that straight down output either. That's a good point. If you have 1 of those filters it doesn't matter where the water line is. From a filter performance perspective, that is.
 

MomeWrath

Member
In my 75 I have an AC110 hung on the right side end of the tank. When the tank is full up I get zero surface scum, no bubbles in the water, and just a quiet riffling of the surface right at the bottom of the filter output and traveling about 2/3 across the tank. I can tell there is more surface movement because I have 2 COB LED gooseneck lights (no lids), and when the tank is full the reflection on the ceiling shimmers like crazy. When the water level drops, there is a very distinct (annoying!) bubble pattern beneath the filter output, and the lower the water gets, the bubbles are angled more steeply down and don't travel as far out into the water column before returning to the surface. The reflection on the ceiling also gets calmer at the other end of the tank. Also, if I leave the water level low for a couple of days, there is the beginning of the surface scum at the end of the tank opposite the filter. So for those reasons I always try to keep it filled up. I haven't done anything specifically scientific, those are just my observations. I'm sure that the water isn't only moving in a little circle right in front of the filter, but the turbulence certainly seems more localized and things move less at the other end when the water is low.
 

Momgoose56

Member
Dave125g said:
Yes 8.2 pounds per gallon. I use 10 because it's easier to multiple. Moving a tank with water in it can cause seals to fail. You can level your tank with water if you want. But I would rather not have 125 gallons of water flooding my living room.

Again this is off topic. On topic. Thanks for the ballistics lesson, and the complement. I do think your comparing apples to oranges though.

I addressed oxygenation in the first post. In addition to an airstone....live plants are really all you need. But if your not into that, an output below the water line provides enough surface agitation. If not I'd say your under filtered.

As far as a test. Not exactly. I'm not I scientist so I haven't used a proper scientific method. However I keep Italian vals. I have observed there movement with the water line above and again below the filter output. That's how I came to my conclusion. You may call it a hypothesis if you wish.
Well, that makes sense. You would see more plant movement with water movement spreading out below the surface and not so much with water spreading out on the surface. This is how I think the water would move:

Sorry, i'm right handed but it works worse than the other one now so I've had to learn to write left handed- pretty sloppy!
I'll test it the dual "hypotheses". I have a 30 g with a HOB that needs a water change. I just have to find something that is semI buoyant around the house...Mung beans maybe? Dried garbanzos? lol! I LOVE experiments! I'll see if I can video the results but i'm going to have to ask how to post one. I've never posted a video before...:rolleyes:
 
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Dave125g

Member
Momgoose56 said:
Well, that makes sense. You would see more plant movement with water movement spreading out below the surface and not so much with water spreading out on the surface. This is how I think the water would move:

Sorry, i'm right handed but it works worse than the other one now so I've had to learn to write left handed- pretty sloppy!
I'll test it the dual "hypotheses". I have a 30 g with a HOB that needs a water change. I just have to find something that is semI buoyant around the house...Mung beans maybe? Dried garbanzos? lol! I LOVE experiments! I'll see if I can video the results but i'm going to have to ask how to post one. I've never posted a video before...:rolleyes:
Your drawing depicts a filter output pointing straight down. Is that how yours works?

Post your video to YouTube then post a link here.
 

Momgoose56

Member
Dave125g said:
Your drawing depicts a filter output pointing straight down. Is that how yours works?

Post your video to YouTube then post a link here.
It's a HOB. The water falls straight down, like a waterfall, as with all HOBs I thought... I see what you're getting at though, if the outlet is below surface level, the water would dissipate outwards faster, rather than straight down. Right! My drawing doesn't take that into consideration as yours does! I'll do the experiment sometime today and post tomorrow
 
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Dave125g

Member
Momgoose56 said:
It's a HOB. The water falls straight down, like a waterfall, as with all HOBs I thought... I see what you're getting at though, if the outlet is below surface level, the water would dissipate outwards faster, rather than straight down. Right! My drawing doesn't take that into consideration as yours does! I'll do the experiment sometime today and post tomorrow
No. Quality HOBs have an output that goes across the top. That was discussed a few posts back.
 

jpm995

Member
Don't most tanks have a decorative ring around the top edge so you don't see the water line? Mine has room for a 1/4 inch leveling error.
 
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Dave125g

Member
jpm995 said:
Don't most tanks have a decorative ring around the top edge so you don't see the water line? Mine has room for a 1/4 inch leveling error.
Most tanks have a frame yes. It's not that big. My big tanks frame is only about an inch wide.


Here's a video of a val leaf showing the current.
 

Momgoose56

Member
Dave125g said:
No. Quality HOBs have an output that goes across the top. That was discussed a few posts back.

This is a standard HOB.
 
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Dave125g

Member
Momgoose56 said:

This is a standard HOB.
Penguin biowheal? I got 1 on my 40. It has the lip on the bottom to direct the water across the top. Yours does too
 

Momgoose56

Member
Dave125g said:
Penguin biowheal? I got 1 on my 40. It has the lip on the bottom to direct the water across the top. Yours does too
Okay, I see what you're saying, if that curved lip were submerged, water would flow out from it as opposed to it falling straight down (because gravity sucks) when the water level is lower. No arguement there. I amend my drawing:
 

Rcslade124

Member
I have my hob in my 29 g towards the left to try and let my jetlifter push as far across the surface to agitate the water more. But I am seeing a lot of micro bubbles from the hob so I'm def going to try and fill my tank to the hob and see interesting thread.
 
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Dave125g

Member
Momgoose56 said:
Okay, I see what you're saying, if that curved lip were submerged, water would flow out from it as opposed to it falling straight down (because gravity sucks) when the water level is lower. No arguement there. I amend my drawing:
Yep there it is.
 

Kevin1962

Member
mattgirl said:
Me too !!!! my 55 is about 1/4 inch lower on the right side so I have to live with a tiny water line. I have learned to live with it but wish it weren't so :( But I always keep my tanks filled high enough to keep the HOB's output below the water line.
My tank is 2mm low on the left and if I can see the waterline I think about reshimming the stand. So of course I fill so I can't see it.
 
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Dave125g

Member
Kevin1962 said:
My tank is 2mm low on the left and if I can see the waterline I think about reshimming the stand. So of course I fill so I can't see it.
Tough to get it any closer then that.
 

DoubleDutch

Member
Only doubting the waterflow comes like your two drawings Dave.

In the first I'd expect it not directly go down to the inlet and if the second would be correct there would only be circultation between the in and outlet still leaving 90% of the tank unfiltered.

But I still think the second is better.
I think even for aeration it is better (waterflow in the tank is more important than falling water into it)
 

Kevin1962

Member
Dave125g said:
Tough to get it any closer then that.
The stand is as close to perfect as 2 days of shimming could get it. Levels on the bottom glass say it's level.
Marineland trim? Not so much.
 
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Dave125g

Member
Kevin1962 said:
The stand is as close to perfect as 2 days of shimming could get it. Levels on the bottom glass say it's level.
Marineland trim? Not so much.
I have never been able to get my tanks perfectly level, so I simply try to get them to lean slightly toward the wall behind it. That way if it tips(for some odd reason) the wall stops it. Hopefully.
 

John58ford

Member
There is some merit to both lines of thought to be honest. However, no when water falls from a distance closer than terminal velocity, it does not lawn dart straight back down to the intake tube. (Ever throw a water balloon at a pool and see it splat right open in all directions, not sink?) On the other hand, the closer to the water line your outlet is, up until it touches, the pump had less static head to overcome and the gallons per hour will sightly increase.

Things change once you submerse an outlet however, then there is a presence of a slight back pressure (due to gravity of the tanks water, resistance and convergence), and surface tension will no longer be in your favor, there will be a decrease in gph upon submerging any filter types outlet. There's also the chance of tank stock or snails finding their way in allot easier.

As allot of people say, there is merit to testing various levels and setting your tank up the best way you can to meet it's specific needs. The idea to use semI Buoyant items, such as fish pellets to see your flow is a good idea and most people should give it a try.

Thanks for opening this post, if for nothing more than to encourage some thought.
 

Momgoose56

Member
John58ford said:
There is some merit to both lines of thought to be honest. However, no when water falls from a distance closer than terminal velocity, it does not lawn dart straight back down to the intake tube. (Ever throw a water balloon at a pool and see it splat right open in all directions, not sink?) On the other hand, the closer to the water line your outlet is, up until it touches, the pump had less static head to overcome and the gallons per hour will sightly increase.

Things change once you submerse an outlet however, then there is a presence of a slight back pressure (due to gravity of the tanks water, resistance and convergence), and surface tension will no longer be in your favor, there will be a decrease in gph upon submerging any filter types outlet. There's also the chance of tank stock or snails finding their way in allot easier.

As allot of people say, there is merit to testing various levels and setting your tank up the best way you can to meet it's specific needs. The idea to use semI Buoyant items, such as fish pellets to see your flow is a good idea and most people should give it a try.

Thanks for opening this post, if for nothing more than to encourage some thought.
Fish pellets!! I haven't found anything that works (but I've been trying different beans-3 different lentils, anasazi, dried chick peas, even freeze dried rice... etc.) But all are either too buoyant or too dense. Slow sinking pellets would work! I have to get some...
 
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Dave125g

Member
Best way to test it is in an empty tank with food coloring put right into the HOB. You'll be able to clearly see where the water goes out of the filter output.
 

John58ford

Member
Dave125g said:
Best way to test it is in an empty tank with food coloring put right into the HOB.
I have done this on many more complex set ups and couldn't agree more. You can also use water conditioner in the right lighting for a similar effect.
 

Momgoose56

Member
Dave125g said:
Best way to test it is in an empty tank with food coloring put right into the HOB. You'll be able to clearly see where the water goes out of the filter output.
I do have a 10 gallon 'dry docked' QT tank. Lol! I'll have to get liquid food coloring and an assistant (granddaughter) for a liquid test. Plus the you tube stuff. My minor was Informatics but I have no idea how to upload videos onto you tube!
 
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Dave125g

Member
John58ford said:
I have done this on many more complex set ups and couldn't agree more. You can also use water conditioner in the right lighting for a similar effect.
Yeah that has a bit of a shimmy to it when adding it to water.
 

aussieJJDude

Member
A lot of this could be solved with some DIY ingenuity. A rew aquarists set up their hobs by adding PVC and some elbows so the intake is on thr opposite side to the outake, like a glorified hang on canister....
 

mattgirl

Member
Just some of my observations....

I have to think my 2 HOB's and 2 dual sponge filters in my 55 gallon tank circulate the water as much as is necessary. All of the filters are across the back of the tank. dual sponges in each back corner and 2 HOB's equally dividing up the space between the sponges. When I add liquid ferts I normally squirt them in a front corner. It kinda shimmers so I can watch it as it almost immediately spreads throughout the tank.

Although it appears that the water falls straight down from my cascade 300 hob filters it actually doesn't. The proof is the fact that floating plants are pushed to the front of the tank. Then kinda circle around and end up in the back under the filters only to either be pushed under the water or right back to the front again. Without being corralled the floating plants are constantly on the move.

I try to keep the hornwort contained on the left side of the tank but often stray sprigs end up at the other end of the tank. Sometimes on top but often tangled in the low growing plants on the right side toward the front of the tank. This is telling me that there is constant movement throughout the tank and I think a lot of it can be attributed to the fact that I keep my tank filled to the top. When doing water changes the output is of course above the water line. During that time any loose plants stay where they are in the tank but are pushed straight down. This tells me that there is less circulation during that time.
 

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